Sleeping Bag Liner Question

[Just Bill]

I got a PM that I have gotten a few times, so thought I'd share it and my response with everyone to both answer the question and let us discuss it openly.

"Planning my 2017 thru and was going to buy a moderately rated bag but high quality Sea to summit bag and use a bag liner for the first part of my hike as I plan to start early March.
That being said do you think my idea is completely dumb?"

I will say though that using a bag liner can have some advantage in keeping your primary bag (especially down) clean. Though it will do little more than add a few degrees for a silk weight liner.
I will also say that a VBL (vapor barrier liner) can have some interesting and great properties- but that's another topic.

So: To this point (which I once thought was a good one)- Can a Sea to Summit liner extend the temp rating for a spring start?
I would call it a dumb idea... though only because I once had the same brilliant idea before and have since not only tried it out- but learned more of the science/common sense behind why it's a dumb idea.

We've all come to agree (generally) that the Sea to Summit liners are (being generous) rated at least double their actual performance in the field. That's probably enough to discount them, but I do better understand why they end up this way since getting into sleeping gear commercially. Let's look at the main example:https://www.rei.com/product/797114/s...ummy-bag-liner

The STS Thermolite Extreme claims up to 25* of warmth added to a bag at 14 ounces.
For most of us... we get the liner and it doesn't work as advertised and we call it a day.
For some of us... we look a bit harder and see it's basically a sack made out of long underwear material (silk to thermal weight depending on the model).

We then may realize that a pair of long underwear weighs about the same as that liner... or that we'd rather carry a puffy (vest/jacket, down/synthetic) and that that does more for us per ounce than the liner ever would.
And we can wear it outside our sleeping bags.

You also might look around and realize that you could buy an ultra high quality down bag that is less than 14 ounces.
Or you could look at that SUL synthetic quilt you made for the summer time that only weighs 12 ounces and realize you could simply carry that and pile it onto your shoulder season bag and that it legitimately does add 20+ degrees to your sleep system. Compare either of them "face to face" in your hand and you'll wonder how you ever thought that a liner could equal the warmth of an actual summer weight quilt/bag.

If you wanted to nerd out a bit: you'd get into the CLO values as this is synthetic insulation- https://en.wikipedia.org/wiki/Clothing_insulation
You might see that EN ratings call a pair of midweight thermals (pants and bottom) along with socks and a matching hat (beanie) are ALREADY included in the rating system as being worn by the user.
You might also note that these layers add about .5 CLO or 3* to the system as a whole. So even a thermal weight layer adds at best 1 CLO or about 5* F depending on the testing method.

If say you were bothered by this problem and looked into it a bit more (like say you were making sleeping bags for SUL/Speed hikers)...

So you might wonder how it's physically possible that you could even attempt to call this product as adding 25* of warmth.
You'd try to find a value for Thermolite and realize it's a bit tricky to find out.
https://thermolite.com/en/Technologi...ies/DUAL-LAYER

An old BPL thread lists the CLO value as high as .598 fabrics. https://backpackinglight.com/forums/topic/42340/
Thermolite's page lists them as 25-30% higher than denim. Denim is generously about .3 CLO, so that would put you at .39 CLO if being generous again.

Even if you give them .598 CLO per 100GSM (grams per square meter or 3 oz/yard) sample, that's a bit lower than Thinsulate 100GSM insulation which posts about .79 CLO total.
This is at best (when combined with other layers and getting a boost as a liner) a 5* bump at 1CLO.

Climbashield Apex is .82 CLO per ounce. So an equivalent 100GSM is 2.46 CLO or roughly 45* (EE rates their 1.64 CLO Apex Prodigy at 50*)
Primaloft Gold is .93 CLO per ounce. So an equivalent 100GSM is 2.79 CLO or roughly 42* (EE rates their 3.28 CLO Apex Prodigy at 40*)

You would need 4-5 layers of thermolite to equal the same insulation value in CLO as either of these products.

So nerd story short...
1- It seems physically impossible for the STS liners to ever achieve anything close to the ratings they claim- even cut in half as we used to say.
2-Further when you consider the weight of the liner itself, you could do better with either a puffy jacket or an extra sleeping bag.
3-Recent innovations and some effort by many folks (Enlightened Equipment especially) have helped to show that a 45* bag laid over any other bag will add roughly 25* of warmth to a sleep system.
(I'm finding that with my personal gear... that it is safer to take about 5* off their formula)

So yar- the Sea to summit liners for warmth are dumb.
1- bring a puffy jacket you can sleep in or better yet lay over your sleeping bag to stretch it.
2- bring a summer weight quilt for roughly the same weight to achieve that level of bump in temps to your sleep system.
3- if buying new- bumping up the temp rating of your base bag (and/or using a quilt) will weigh far less than adding a liner. In a quality down bag, you're typically talking 4 ounces or less of down to jump 10-15* in rating... much less weight than any option.

Now besides the fact I plan to sell them... I prefer the quilt as there is a way to convert it to an acceptable camp puffy in combo with my wind shell... so I get the best of both.

Though for the AT spring starter specifically- I think that a quality 20* mummy bag and a summer weight synthetic quilt are the far better/cheaper system overall.
Use both at the start and have the protection of a good mummy bag in truly cold temps with a synthetic quilt over the top to protect the down layer.
As it warms up a bit- send home the summer quilt and carry the mummy. As you hit VA and things warm up, swap out for your summer quilt and then reverse that as you approach August and/or the whites.

Two bags total covering your whole trip. 20* down mummy and a 45-50* summer quilt puts you at around zero at the start of your trip for about the price of one really good zero degree down piece.


PS... I'd be pretty skeptical of the Sea to Summit Spark series too.
http://www.seatosummit.com/wordpress...9_16_FINAL.pdf

[DuneElliot]

Well-laid out argument, and I completely agree with your assessment...I'm just too lazy to write it out.

[Slo-go'en]

I like using a liner. While not cheap, a silk liner doesn't add much weight or space to your pack. Besides keeping your bag clean, it reduces drafts, it can be used in hostels which supply blankets but not enough of them and in the summer it can be all you need for most of the night.

[One Half]

I have to say, this is great timing for me as I have been thinking about adding a liner and "weighing" the pros and cons. I love how well you laid that out, explained the truth behind the claimed ratings. I thought I was simply not comprehending something when I started looking at the liners. Thank you. You have helped me make the decision I was leaning towards - not getting a liner.

[rafe]

As opposed to silk liner, also consider just a silk base layer, for camp and for sleeping only. Weighs very little, so the "warmth per ounce" is quite high. Washes easily, air-dries quickly.

[Just Bill]

As opposed to silk liner, also consider just a silk base layer, for camp and for sleeping only. Weighs very little, so the "warmth per ounce" is quite high. Washes easily, air-dries quickly.

Dutch seems to have beat me to it... so for what it's worth- http://www.dutchwaregear.com/quilt-liner.html

I've been toying with doing the same thing with my shell material from the quilts. It'd be about the same weight- though since Dutch has no specs- no idea on the exact size comparison.
Though an educated guess is he simply used roll width by 7' long for a blank so the finished liner would be about 28" x 80" flat- matches the 2.5 oz weight spec.

Basically a "synthetic" silk liner but since the fabric is calendared and has a DWR it would also make an acceptable SUL splash bivy/cover or a windshell for your sleep kit.
But yes- that material packs to about the size of a baseball and fits in your pocket. I was designing it for a fella contemplating a 24 hour race in warm weather looking for a minimal option for a crash nap.
My prototype has a drawstring footbox on it to vent as a hot weather sheet (but no zipper) and a more traditional mummy shape and a bit more height to it (so you could pull it over your head for sun or skeeters).

But as far a simple MYOG projects it looks like Dutch basically took a rectangle, hemmed all the sides, folded it up so the ends met in the middle and sewed up the bottom and a bit up the side to make a footbox.


Though I prefer Kyle's Membrane 10 https://ripstopbytheroll.com/product...affeta-nylon-1
With 3 yards ($30) worth of material you could make one of those and have enough material for 4-8 pretty nice SUL stuff sacks (playing with that too, these come in about the same as Cuben .50 (no tape) for a third of the cost).

Yar- it ain't silk- but it's as close as you get with the added benefit of it working a bit like a windshell if used as an outer layer.

[Dogwood]

Well, you would be labeling me as dumb because as one of my options, depending on a range of considerations, I leave open the possibility of using a Cocoon or Sea to Summit SILK Liner or other possible liner to augment sleep systems while possibly a liner having a greater range of usability beyond just inside a sleeping bag to add warmth. It depends on a range of what I'm attempting to achieve in what I opt for and how I pair the liner. Saying it another way, it's not a clear cut duality of good and bad choices - Liner GOOD Liner BAD - Fire GOOD Fire BAD. Context and perspective count! Moving away from myopically seeing the world, or specifically gear options in this case, has added to a greater selection of possible approaches and solutions. It can lead us to be a better thinker, examiner, surveyor and more tolerant to a wider range of options. You eventually got there toward the middle of your initial post.

Look carefully at what the marketing claims. 'The STS Thermolite Extreme claims up to 25* of warmth added to a bag at 14 ounces." Perhaps liner companies are leaving some wiggle room as far as quality of their specs but let's be fair up to does not mean this liner WILL add 25* of warmth. It means it possibly can.

"For most of us... we get the liner and it doesn't work as advertised and we call it a day." This is common, taking oneself out of the performance equation by ignoring varying degrees of personal/user responsibility. We've heard it so often. WP shoes are bad. I effectively employ WP shoes. That rain jacket sucks. Rain jackets don't work. Just get wet. Rain jackets are necessary. Single wall tents suck. Bivies are bad. Bivies can be great. UL sucks. UL is great. Again, context, details, and perspective count.

When gear wt becomes a overriding priority in what one possibly can achieve, getting a 25* warmth bump in the sleep system, by amending with an additional 14 oz piece, this is where we agree. There are other approaches, BASED ON WHERE YOU AND I LIKELY HAVE CURRENTLY EVOLVED TO, and maybe how we similarly gear up and think, that can get us there with a lower wt penalty. Don't get this twisted, but all people all hikers are not equally in the same place, need to be, or want to be. Each approach is not right for all people all the time.

Where I recognize greater use for myself in a liner that is a more acceptable wt trade-off for what I potentially receive is optimally user employing a 4 oz SILK MUMMY LINER W/HOOD W/HOOD TIE getting a possible 4-7* sleep system warmth bump using an advanced UL LD backpacking approach. Since we're talking specs I like to compare warmth to wt ratio comparisons while also considering a variety of other possible uses of a liner, like draping it over my shoulders and around my torso WHEN HIKING for added warmth on a limited basis or avoiding drafts using an UL highest end down quilt where I'm rotisserie sleeping or avoiding or avoiding/decreasing heat loss as a cowboy camper. Considering these ratios at this wt and type liner, with it's compqacvtability, and in line with teh way I approach hiking, and in context of possible greater usage for what I receive, is often more easily digested as a ULer.

What I also have long ago gotten away from that is beyond the main topic of the thread is assuming I have to consider gear as my only or primary source of approaching solutions to issues like sleep system warmth. An over reliance on gear and falling into the cultural trap that throwing money at an issue is the way to address issues ignoring possible world changing useful knowledge and skill set utilization is all too common among gear junkies. I include myself in falling prey to this and have since recognized it and are further moving away from a materialistic gear solves all problems mindset.

[KDogg]

I used a liner most of the trail. It did add "some" warmth but primarily it was to keep my quilt clean. I don't like to sleep in a bag as it feels confining to me. The liner felt very versatile, was not confining, and I could wash it when it needed. The particular liner I ended up with (more because it was the only one available when I looked) was permethrin coated. Not really sure if the permethrin worked or not but I don't feel that I got bit up much at night. If I got cold I put on more layers, when it was hot I took off layers and slept in just the liner. I never slept in just the quilt. I find the fabric of, so-called, ultralight quilts and bags to be uncomfortable to the touch. My liner on the other hand was very soft. I started on the 31st of March with a 40 degree quilt and the liner. Got too cold once but survived. My liner was an integral part of my sleep system and I will take it with me if or when I hike again.

[rickb]

A silk liner and a boa constrictor have a great deal in common.

[handlebar]

i've been using STS or Cocoon silk liners on all my long distance hikes, both to help keep my down sleeping bags clean so they keep their loft and to add a few degrees to the rating. I find they add about 5 degrees. I recently finished a chunk of 815 miles on the NCT starting in the Adirondaks in late Aug and finishing up at the end of Allegheny National Forest using a 30* WM Summerlite and a STS mummy silk liner. A couple nights it got as cold as 30* and I found that carrying my down sweater added enough insulation to keep me comfortable. (I interpret the degree ratings on sleeping bags as meaning, "you won't die" not that "you will be comfortable".) Ten years after my AT thru I would start out a mid-March nobowith the same set up I had on the NCT and plan to use the down sweater for cold nights, switching to a summer bag with silk liner after Mt Rogers. I used the silk liner as a sheet to cover my sleeping pad on those hot mid-Atlantic nights and left the 45* bag open so I could pull it over me when/if the temp got low enough to wake me.

[Wise Old Owl]

I like using a liner. While not cheap, a silk liner doesn't add much weight or space to your pack. Besides keeping your bag clean, it reduces drafts, it can be used in hostels which supply blankets but not enough of them and in the summer it can be all you need for most of the night.

Please try to understand and take a moment to read the post check the links. The starting post had nothing to do with a Silk Liner.

OH and Just Bill, great post... I am on the fence, a VBL will stop a high wind robbing you of heat thru the night. It works better than a fleece and extra clothing.. In short in high cold winds a tarp, a reflective, a reflectix,a closed cell foam barrier makes a world of difference in 35 mile winds.

I hope I gathered and understand the thread - I feel a few missed the opportunity of VBL. No Biggie!

[Another Kevin]

I think that a quality 20* mummy bag and a summer weight synthetic quilt are the far better/cheaper system overall.
Use both at the start and have the protection of a good mummy bag in truly cold temps with a synthetic quilt over the top to protect the down layer.
As it warms up a bit- send home the summer quilt and carry the mummy. As you hit VA and things warm up, swap out for your summer quilt and then reverse that as you approach August and/or the whites.

Two bags total covering your whole trip. 20* down mummy and a 45-50* summer quilt puts you at around zero at the start of your trip for about the price of one really good zero degree down piece.

Sounds sensible to me. I haven't tried bag+quilt, but it sounds as if it'd work as long as the weight of the quilt doesn't wreck the bag insulation by compressing the down. I have a 0° bag, and I don't often get out when it's colder than that. (If need be, I push the rating a little by wearing my fleeces in the bag and spreading my puffy out on top over my core. I've gone down to minus single digits comfortably that way.)

In really cold weather, don't forget that the insulation under you is even more important than the insulation above you. When I bring my 0° bag (not a really good one - a Marmot Never Summer), I generally bring my ProLite, plus a blue foam, plus possibly a car sunshade, and put my empty backpack under my feet as well. At least until the raccoon drags it away.

I wonder how that Argon fabric would work as a vapor barrier. It appears at the moment that my endurance limit in winter is set by the accumulation of condensation in my sleeping bag. The Argon material is advertised to be 'breathable' which doesn't bode well. Probably better to do the experiment by sucking it up and humping the 11 ounce one from Campmor.

[Dogwood]

Please try to understand and take a moment to read the post check the links. The starting post had nothing to do with a Silk Liner...

Umm, JB was certainly including silk liners in his talk about liners. Read his two posts.

Then he went into analyzing one specific liner the STS Thermolite Extreme.

He was responding to answering an email he received by a person anticipating a thru-hike who was pondering "Planning my 2017 thru and was going to buy a moderately rated bag but high quality Sea to summit bag and use a bag liner for the first part of my hike as I plan to start early March.
That being said do you think my idea is completely dumb?"

From what we know based on available info or can infer the question was asked by someone sending an Email to JB concerning use of a bag liner....any kind of liner. There's no indication in the Emailer's excerpt that a 25* increase in sleep system warmth had to be achieved or if the Emailer wanted to achieve a 25* greater warmth by liner supplementation alone. BTW, who says adding sleep system warmth can only be approached by throwing a liner into the sleep system mix anyway? That was one of JB's main analyzed points, was it not? Why does it have to be the STS Thermolite Extreme liner that's chosen? Why can't a warmth bump be approached in several ways all at once that might include a liner? Even if providing a total 25* warmth bump was intended why can't a liner be part of the solution...at last for some folks...even by employing a liner NOT specifically marketed for adding all of the 25*? And, since when is achieving more warmth always about more gear or need to be approached from that narrow gear junkie perspective? Achieving additional warmth to sleep goes beyond just throwing gear at it. OMG, so many tricks, techniques, etc that can be utilized IF knowledge from skills also enters into the greater sleep warmth equation. No?

This is the exact type of situation I was referring when stating context, details, and perspective count. JB goes into analyzing one specific liner brand and type, at least initially, where he makes some good points factoring in liner weight compared to other possible approaches in context of the trade offs when the main goal is to raise sleep system warmth and folks start making generalizations about all liners. And even JB jumps on the bandwagon. It's the same when talking about WP trail runners or bivies or rain wear. All liners are not the same. All liners aren't the STS Thermolite Extreme. Different liners have different characteristics and features. Hence specs are different. Hence analysis of each liner is required. Hence, different conclusions could possibly be reached on what is deemed "completely dumb." There are lots of combinations and possibilities here. To judge or make hard and fast conclusions on one possible scenario of many leaves me thinking but, what if, could be, depends....

[Just Tom]

Dutch seems to have beat me to it... so for what it's worth- http://www.dutchwaregear.com/quilt-liner.html

I've been toying with doing the same thing with my shell material from the quilts. It'd be about the same weight- though since Dutch has no specs- no idea on the exact size comparison.
Though an educated guess is he simply used roll width by 7' long for a blank so the finished liner would be about 28" x 80" flat- matches the 2.5 oz weight spec.

Basically a "synthetic" silk liner but since the fabric is calendared and has a DWR it would also make an acceptable SUL splash bivy/cover or a windshell for your sleep kit.
But yes- that material packs to about the size of a baseball and fits in your pocket. I was designing it for a fella contemplating a 24 hour race in warm weather looking for a minimal option for a crash nap.
My prototype has a drawstring footbox on it to vent as a hot weather sheet (but no zipper) and a more traditional mummy shape and a bit more height to it (so you could pull it over your head for sun or skeeters).

But as far a simple MYOG projects it looks like Dutch basically took a rectangle, hemmed all the sides, folded it up so the ends met in the middle and sewed up the bottom and a bit up the side to make a footbox.


Though I prefer Kyle's Membrane 10 https://ripstopbytheroll.com/product...affeta-nylon-1
With 3 yards ($30) worth of material you could make one of those and have enough material for 4-8 pretty nice SUL stuff sacks (playing with that too, these come in about the same as Cuben .50 (no tape) for a third of the cost).

Yar- it ain't silk- but it's as close as you get with the added benefit of it working a bit like a windshell if used as an outer layer.

How do you think this compares (warmth / comfort or feel / weight / breathability / etc) to the liner made by MLD based upon materials used and what not? http://www.mountainlaureldesigns.com...roducts_id=169

[Firesong]

Argon is a calendared nylon. It breathes still and wouldn't work as a vapour barrier. We use it as an 'UnderQuilt protector' fabric as well to slow the wind down and use its
DWR to keep the moisture off the quilts.

[Just Bill]

Well, you would be labeling me as dumb because as one of my options, depending on a range of considerations, I leave open the possibility of using a Cocoon or Sea to Summit SILK Liner

DW- We're on the same page mainly. Call it poor wording on my part but the second line or so sums up my feelings on a silk liner (first line below). For 2-4 ounces I do consider a versatile piece of gear as well. Much like a wind shell can do more than people realize as a windshell. However as a jacket under other layers it has little thermal value as an insulation piece. It's a perfect example of something that could PRESERVE 10-20* of warmth when used as a shell it cuts out most convective heatloss and creates a minor micro climate as a SEMI-VBL. However if you simply wear it in your sleeping bag- it has zero thermal value beyond any silkweight layer (.25 CLO or 1-2*)

I will say though that using a bag liner can have some advantage in keeping your primary bag (especially down) clean. Though it will do little more than add a few degrees for a silk weight liner.


So: To this point (which I once thought was a good one)- Can a Sea to Summit liner extend the temp rating for a spring start?

The premise of the thread is bolded just above... addressing the question of if you could truly buy a THERMAL LINER and achieve the claimed warmth to the total system.
Not the value or performance or utility of various liners but the specific claim made by STS that you could buy their liners and add 10-25* to a bag.

Look carefully at what the marketing claims. 'The STS Thermolite Extreme claims up to 25* of warmth added to a bag at 14 ounces." Perhaps liner companies are leaving some wiggle room as far as quality of their specs but let's be fair up to does not mean this liner WILL add 25* of warmth. It means it possibly can.

That's sorta the main premise of the thread- looking carefully at the marketing claim. Our old rule of thumb was to cut the STS ratings in half- across the line.
Having since learned more I'm saying that this liner will not likely even deliver half. No wiggle room- no possibility. T

hey are basically using a knock off of Thinsulate... which much like a windshell can do some neat things in the field if used in the correct location (exterior shell like hat, glove, or ski wear)- but thinsulate is very inefficient compared to other insulations for use in sleeping gear by a wide margin. I think that they are basing their claim very much on the claim you or I might make with a windshell. In the perfect application it may do what we say, and in the lab as a single layer Thinsulate style insulations could be shown to serve as an insulator. But as a liner or insulation piece in a sleep system... not even close.

Sounds sensible to me. I haven't tried bag+quilt, but it sounds as if it'd work as long as the weight of the quilt doesn't wreck the bag insulation by compressing the down.

A few years back, there were some extensive conversations on this topic at Hammock Forums and BPL. The topic had to do with the mysteries of overstuff/overfill. Long story short- it was shown that compression of down to even as much as 75% ideal loft showed little loss in performance... a few people even claimed that a bit of compression could slightly improve performance (but that's a bit sketchy and has to do more with correcting an underfilled bag in my opinion as the extra fill would eliminate shifting in a "perfect" fill once the less than perfect conditions of the field prevented ideal loft of down.)

Now if you're talking the less scientific "fit" of stacking quilts- yes if you crammed an ill fitting combo together and mashed the loft you'd have a problem. Bit like the old "cold shoulder/hip" issue for side sleepers where those pointy protrusions reduce loft at those high points. That said, Peter at Enlightened Equipment, had mentioned during our quilt stacking discussions here that he had no issues in the field with stacking equal sized down pieces. Unlike synthetics down has a way of morphing to fit (especially in a quilt). Mummy bags are a bit more tightly controlled in baffle design.

My synthetics though do need to be differentially cut to stack properly for synthetic over synthetic. But synthetic over down... a quilt is usually more generously cut than a typical mummy bag- but yar if you crammed a 40" diameter foot box of a mummy into a 36" synthetic quilt you would definitely have cold feet... so a bit of care is needed there. Up top you'd see no real issues other than the quilt sliding off you in the night.

How do you think this compares (warmth / comfort or feel / weight / breathability / etc) to the liner made by MLD based upon materials used and what not? http://www.mountainlaureldesigns.com...roducts_id=169

Argon is a calendared nylon. It breathes still and wouldn't work as a vapour barrier. We use it as an 'UnderQuilt protector' fabric as well to slow the wind down and use its
DWR to keep the moisture off the quilts.

I wonder how that Argon fabric would work as a vapor barrier. It appears at the moment that my endurance limit in winter is set by the accumulation of condensation in my sleeping bag. The Argon material is advertised to be 'breathable' which doesn't bode well.

This sorta brings it back full circle then....
Dogwood is correct- a silk weight liner will add a few degrees to your sleep system. Though unless you are truly pushing things and sorting out those few degrees I would advise the average user to ignore that bump. However a liner under a quilt would do much for a new quilt user as it would help you manage drafts better before you got the hang of it. I personally do not like or use liners.

Now two materials are being discussed....
.67 oz/SY 10d nylons. Membrane 10 from RBTR is what I use. Dutch has his Argon, Thru-hiker sells Momentum 50, MLD has their own version, so does EE.
They are all basically the exact same material... a Nylon that comes in either Taffeta (no RS grid) or with a small ripstop grid. (ARGON comes in both)
This is basically a version of the material that comes in a Houdini or similar windshell. It's basically the SUL version of any sleeping bag liner you've ever used.

On it's own- it's basically synthetic silk. Similar properties/performance.
It can then be calendared (I believe they all are) with helps with wind resistance and helps the fabric achieve a "down proof" rating so it can be used in sleeping bag shells.
It is often then hit with a DWR... mainly to help achieve that downproof rating from what I understand as otherwise you'd not waste the money on applying it if you simply wanted a sleeping bag liner.

So this product (Dutch/MLD/whatever) can serve well as a sleeping bag liner or as Dutch cleverly figured out- as a WINDSHELL for your sleeping bag. Basically a wind-bivy.
In that application, much like a windshell it could provide a fairly large bump in temps (or perceived comfort in those temps). If you were cowboy or tarp, or even shelter camping with any kind of breeze- using a windshell for your bag makes as much good sense as using a windshell when moving. However other than keeping your bag clean and/or preventing some drafts- it has little to no value (thermally) as a liner.

I forgot about the MLD product- which is cut as a liner for a Men's med/lg size and meant to be a liner. However what I was shooting for was more along the line's of what Dutch came up with as it would do all the things that Dogwood mentioned, and you could add being able to use it as a windshell/mist bivy on a breezy night. It would work fine as a liner... but for 4 ounces or under could also perform all the things a windshell could.

DWR- DWR is still breathable... only issue with it as a sleeping bag liner is you're probably going to wash it often. 15-30 washings later your DWR goes poof. You stay windproof, but loose that semi-VBL property of trapping enough body moisture to create a more humid micro-climate after a bit. So if you wanted this fabric as a bivy- don't wash it much. But as a liner... once the DWR fades a bit... it's comparable to silk.

To Kevin's question... no a calendared DWR nylon is not a VBL. Period.
You need a fully coated fabric. Silicone or PU coating...
If I were to mess with a VBL... or push that wind bivy/liner principal a bit further...
The fabric I would use would be this- https://ripstopbytheroll.com/products/membrane-silpoly

This is a POLYESTER, not a nylon. And it is coated with silicone, not DWR. This is one of the lightest and best performing versions of this product. It's a SUL version of your standard 1.1oz (1.4 oz finished) Sil-Nylon.
This product has a finished weight of .93oz and more importantly has a better hand feel than Sil-nylon for use as a VBL.

So if I wanted a true VBL... this is the type of fabric you want... though if you want a true VBL that's a different discussion.


One thing I am excited to try when I find time- https://ripstopbytheroll.com/product...oof-breathable
I won't bore you with how badass it is that Kyle has this fabric. This is as good if not better than anything else available and while it may sound expensive to some- it's a pretty amazing price.

However- with this product, the jumps I've made with Primaloft Gold Insulation and some other things I've figured out...
This may put us as close as we've been to the possibility of simply throwing down in your sleeping bag and a very minimal tarp in most conditions.
I can do this material as the shell of my quilts... I don't see any dramatic failures likely with the WPB shell. I don't see any massive moisture build up for lack of breathing.
And even if there were some issues- Primaloft Gold retains better than 90% of it's insulating value when wet.

The only issue I see- all WPB fabrics still have a face fabric- that relys on DWR to work. Once the face fabric wets out, the membrane cannot function properly. But so long as it's doing decently... the PLG insulation should be able to handle the body vapor load even during a sustained downpour. Once it stopped raining... you could sun the bag briefly to chase out the bit that got trapped.

Yes this would be SUL Gear and not for everyone. However what I'm mainly picturing is that PCT or umbrella using hiker.
Toss down a ground sheet to protect your air pad.
PLG keeps you warm.
WPB shell does the job for most wind/water events and your air pad keeps you out of the puddles.
You simply put your umbrella or similar light structure and use your rain cape/poncho/minimal tarp and drape it over both your head and the umbrella for an impromptu bivy.
On mainly dry nights... a 5x5 or so "tarp" made of bug netting could be thrown over the kit.

Want a bit better coverage? Do a basic mini tarp over your head and let your feet fly out.

Some folks have been pushing that system with Event and down. But Synthetic is a better choice, and this WPB (on paper) is better than Event.
So might finally be all the right parts and pieces to put that unicorn together now.

[Another Kevin]

To Kevin's question... no a calendared DWR nylon is not a VBL. Period.
You need a fully coated fabric. Silicone or PU coating...
If I were to mess with a VBL... or push that wind bivy/liner principal a bit further...
The fabric I would use would be this- https://ripstopbytheroll.com/products/membrane-silpoly

This is a POLYESTER, not a nylon. And it is coated with silicone, not DWR. This is one of the lightest and best performing versions of this product. It's a SUL version of your standard 1.1oz (1.4 oz finished) Sil-Nylon.
This product has a finished weight of .93oz and more importantly has a better hand feel than Sil-nylon for use as a VBL.

Thanks for the pointer! As you know, I was talking about an actual vapor barrier - so that I don't need to find a clothes dryer after 2-3 nights in the field in winter because of condensation in the down. I knew there had to be a solution that was lighter than that horrible polyurethane stuff that Campmor uses in their VBLs, or than Stephenson Fuzzy Stuff, and less expensive than UHMWPE/Cuben.

I'll have to experiment, once the cold weather comes. Assuming that it does. We didn't really have a winter last year.

[Just Bill]

Thanks for the pointer! As you know, I was talking about an actual vapor barrier - so that I don't need to find a clothes dryer after 2-3 nights in the field in winter because of condensation in the down. I knew there had to be a solution that was lighter than that horrible polyurethane stuff that Campmor uses in their VBLs, or than Stephenson Fuzzy Stuff, and less expensive than UHMWPE/Cuben.

I'll have to experiment, once the cold weather comes. Assuming that it does. We didn't really have a winter last year.

I still think one of the coolest things about Kyle at RBTR is the fabrics he develops that we wouldn't have access to. Some of the stuff he has is Patagonia levels of product runs to make... and these new nylons are so close to CF in weight that once you add seam tape to the CF weight it's close enough for me at 1/4 the cost and none of the wear issues.

If you were willing to just do a cocoon style liner (no zips or nothing) you could probably get away with a minimalist VBL with that. Literally fold 2 lineal yards in half, sew up the side and one end and you'd get a 27 ish wide by 70" long sack you could slip into. $16-$20 depending on shipping and right bout 3.5 ounces packing to the size of a decent apple. It'd be a bit of a squeeze at the shoulders but not unduly horrible. A zipper would add an ounce and bulk. Though not sure if you'd be able to work a pee bottle in something that tight (which being clueless fella I know you understand that is an actual issue, lol) Though on the humorous side; I guess if you have a pee bottle malfunction you are in a VBL!

That said- I think I got my differentially cut double layer hammock sorted out (the one I was thinking of sending you to test out) and I may have two yards of that material laying round I could stitch up (or send if you were really wanting to try yer hand). On the downside- that's some slippery stuff and tricky to sew. On the upside- it's just a quick and dirty liner to try out so sewing doesn't need to be great and if you pop a stitch.. who cares.

Been working on getting a few piles ready to send... if I find that stuff I'll set it aside for your pile. (afore you get to particular- I need 5-6 yards for a tarp so a 2 yard scrap is destined for the stuff sack pile anyway).

[Dogwood]

We need independent standardized EN ratings for liners.

In regards to Ron's or Dutch's various nylon liners one performance category where silk has it over both is skin feel. Another important aspect especially under changing sleep scenarios is the ability of silk to respond nicely to temp changes. Although I have no data to back this up I'll also assume silk/ripstop silk is far more breathable than Momentum 50 or Argon .67. Add DWR's to silny or a poly and that decreases breathability as well. As Cocoon states, "high quality silk is the optimum fabric for minimizing packing size and weight. Silk is breathable, soft to your skin and responds well to changing temperatures. It keeps you cool in the tropics and toasty in the mountains.' Taffeta or the Momentum 50 or Argon .67 tends to cling to bare skin. If one has the tendency to sleep with bare skin exposed that might be something to consider. But, since these discussions are heavily significant to and influenced by gram weenie mindsets I'm of the opinion one shouldn't be sleeping with much bare skin exposed as it can show something in the kit isn't being fully utilized or perhaps the cumulative sleep systems temp rating is too high for the conditions which isn't something gram weenies are normally associated.

It seems like Dutch's liner design is in response to his primary market the hammock community. Since some(many?) hangers don't like constricting sleeping bags, are hanging in the air(different ways to think about heat conservation and dumping in terms of gear), and some don't like sleep pads, so under insulation has to be thought out differently, some go to quilts. Dutch's liner seems to me, after only website looks/no personal experience, it's more of a quilt style liner which will appeal to hangers.

Seems Ron's design is attempting to appeal to a few of the specialized piece gram weenies that want to save a couple of ozs by double duty ing up on a design that can be used both as a liner and a over sheet/WR bivy. I'm a fan of both Dutch and Ron but both their designs lead back to the liner question of perhaps in some situations like when greater warmth in cold March temps is required through sleep system augmentation already consisting primarily of a sleeping bag or quilt don't go the liner route and opt for a UL oversheet or UL MLD Superlight, Titanium Goat, etc bivy or maybe Montbell's over bag for the warmth. This optional approach can fit quite nicely into the UL philosophy as now the WR bivy takes on elements of a shelter and tweaks the character of the sleeping bag/quilt from the outside possibly significantly so.

This is hard here on WB to get into this because there's so much more I want to hear and ask about and comment on but the forum isn't the best place for it without inputs of major time resources.

When one asks about augmenting their sleep system with a liner for the primary purpose of adding warmth I immediately want to know details before I can answer. Perhaps a teaching lesson to the questioner expanding understanding can help:

Under what shelter scenario
Sleeping in an enclosed tent is different thermally than sleeping in a hammock or on the ground cowboy camping or tarping under A frame configurations
What core base sleeping bag/quilt is being augmented. Are they using a quilt.
What type of sleeping pad is being used
What type of groundsheet if any is being used
A bump in underground insulation/increasing R-Value even at minimal wt like using a CHEAP reflective groundsheet can add warmth
What is the hiker's skill level and knowledge base
Do they know how to add warmth with various techniques like site selection, do they know how to and when to get out of the wind, do they understand thermal and exposure consequences of sleeping at elevation, do they know how to manage moisture, warm water bottles, emptying their bladder out before sleeping, eating well to fuel the internal furnace, calisthenics, VBL's ....
Utilizing what they already have like gloves, hats, hand pockets, wearing dry rainwear to sleep in, placing feet into empty backpack, spreading anything out underneath them to add insulation
It amazes me how many still complain about sleeping cold with the wealth of sleeping warm info available and when I've seen them elect to use their puffy or dry LS shirt as a pillow rather than wearing it or not wearing dry rain wear or gloves or hats in their sleep or have an used backpack that could be added warmth or eat crappy food that's hard to digest contributing to heat loss or sleep in exposed heart robbing locations on the coldest nights or shelter at an AT lean to yet don't bring into the mix their tent/tarp/hammock for warmth or insulation or don't empty out their baldder before sleeping or will not put some warm bottles of water in their sleeping bag/quilt or opt for the most spacious oversized thermally inefficient sleeping bag when they know they sleep cold or let their down bag's loft be compromised.....

[Another Kevin]

Under what shelter scenario
Sleeping in an enclosed tent is different thermally than sleeping in a hammock or on the ground cowboy camping or tarping under A frame configurations
What core base sleeping bag/quilt is being augmented. Are they using a quilt.
What type of sleeping pad is being used
What type of groundsheet if any is being used
A bump in underground insulation/increasing R-Value even at minimal wt like using a CHEAP reflective groundsheet can add warmth
What is the hiker's skill level and knowledge base
Do they know how to add warmth with various techniques like site selection, do they know how to and when to get out of the wind, do they understand thermal and exposure consequences of sleeping at elevation, do they know how to manage moisture, warm water bottles, emptying their bladder out before sleeping, eating well to fuel the internal furnace, calisthenics, VBL's ....
Utilizing what they already have like gloves, hats, hand pockets, wearing dry rainwear to sleep in, placing feet into empty backpack, spreading anything out underneath them to add insulation
It amazes me how many still complain about sleeping cold with the wealth of sleeping warm info available and when I've seen them elect to use their puffy or dry LS shirt as a pillow rather than wearing it or not wearing dry rain wear or gloves or hats in their sleep or have an used backpack that could be added warmth or eat crappy food that's hard to digest contributing to heat loss or sleep in exposed heart robbing locations on the coldest nights or shelter at an AT lean to yet don't bring into the mix their tent/tarp/hammock for warmth or insulation or don't empty out their baldder before sleeping or will not put some warm bottles of water in their sleeping bag/quilt or opt for the most spacious oversized thermally inefficient sleeping bag when they know they sleep cold or let their down bag's loft be compromised.....

Since I've been in the discussion asking questions:

Shelter: TarpTent Notch with the half-sidewall inner rather than the all-mesh one. Snow banked on the upwind side. I like to pitch on packed snow if possible for additional insulation, and level the pitch with my snowshoes or ice axe if necessary. If there's no snow I try to find a site with thick duff.
Bag: Marmot Never Summer 0° down bag.
Underneath: Therm-a-Rest ProLite, then a blue foam, then a car sunshade. Possibly a piece of Tyvek under the tent floor.
Skill level: "Clueless weekender." In half a century I've probably put in more weekend miles than some thru-hikers have total miles.
Preferred campsite: I try to look part way up a hillside, high enough to get out of the cold sink and low enough to get out of the wind.
Other techniques: I use a hot water bottle so that maybe I'll have water for breakfast that isn't frozen. Moisture management is what winter hiking is all about, and there's always room for improvement. I use my backpack under my feet, wear balaclava and gloves and socks and baselayer and fleecies to bed, and spread my puffy on top of my bag. I still usually use my rainsuit and gaiters in a stuff sack as a pillow because what else do I have to put my head on? If it's colder than I expected I'll be sleeping in, under, or on top of every stitch of clothing that I brought.
I'm sixty years old. Every 60-year-old man knows to empty his bladder before going to sleep.
VBL: I know about them. I use a vapor barrier in my socks. I'm never out long enough in deep winter to risk seriously compromising my geese, but I'm looking to experiment with VBL in a sleeping bag because that's the limiting factor to my winter endurance right now.

I think the biggest single problem that I have with my setup is that I've not worked out how to keep my face to the outside when I'm sleeping. I tend to roll over and bury my face in the sleeping bag hood. Bad news.

In any case, my setup's good enough to keep me sleeping in relative comfort on weekend trips with temps around 0° or a little below. For more extended winter travel I'd need the option to bail out and hole up. Gear that can handle the very worst that Old Man Winter can throw at us in the Northeast - and an extended trip means preparing for the worst - is out of my budget at present, and I really don't have the skills to be out when it's 20 or 30 below. Nor any particular ambition to acquire them. I'm not going to be climbing Denali in this lifetime.