Bag inside of a bag?

[GaryM]

I am looking for a 0 degree bag now and the thought crossed my mind, how would a 40 degree mummy inside of a 30 degree rectangular work out? Or any other combinations.Could you just add up the R factors to get an equivalency? Has anyone tried anything like this?
I am really curious.

[Gambit McCrae]

I have had 2 hiking buddys that did not care to buy bags for the appropriate time of year and in return would bring multiple bags and sleep with on inside the other. Sounds like a nightmare to me but i also have sensory issues. Sounds very constricting

[soumodeler]

I have used a 40* quilt laid over the top of my 10* bag to increase warmth before and it worked great. I was toasty warm in temps somewhere between -5 and 0.

[Slo-go'en]

I've done it. It works. Best for short hikes where bulk/weight isn't a big factor. Not something you'd want to do for long hike.

In my gear closet I have an old synthetic bag desigened specificly as an "outer" bag to extend the rating of the inner bag. By it's self it worked as a loose 50 degree bag. But being synthetic, it's a couple of pounds and a little bulky.

[devoidapop]

As long as neither bag is being compressed, you're adding loft and making the bag warmer. gotta be bulky to carry 2 bags, but hammockers do it.

[Ginger.Snap]

That’s a common enough way to get a cold weather sleep system without buying a specific cold weather bag. Mostly for people who only cold weather camp rarely or don’t mind the extra weight.

Enlightened Equipment has a chart for stacking quilts, I see no reason it wouldn’t be accurate for sleeping bags.

https://support.enlightenedequipment...b-zero-camping

[MuddyWaters]

I am looking for a 0 degree bag now and the thought crossed my mind, how would a 40 degree mummy inside of a 30 degree rectangular work out? Or any other combinations.Could you just add up the R factors to get an equivalency? Has anyone tried anything like this?
I am really curious.

Yes but it depends how much you compress both layers.
One method is to add them together and then subtract 10 degrees.

I have a 30 degree Western mountaineering megalite. It's roomy enough I can put a 40 degree quilt inside of it also. It's a furnace when I do that.

Ive stacked quilts a bunch of times
It's less effective. I've actually had ice in between the two quilt layers, where the temperature was below freezing and froze my respiration through the bottom quilt.

this is why generally when you use an over quilt or such you use a synthetic.

Being honest, its troublesome. That encouraged me to drop $550 for a versalite. Lifes to short to futz around with half arsed solutions

[Pak-Man]

x -(70 – y)/2 = z
x = first bag (higher rated/lower degree)
y = second bag (lower rated/higher degree)
z = rating of doubled bags

[peakbagger]

Works if you are a small person, not so good if you are already filling out the interior of the first bag. As the quilt folks know, the R value of compressed filling be it down or synthetic is pretty minimal.

[TwoSpirits]

x -(70 – y)/2 = z
x = first bag (higher rated/lower degree)
y = second bag (lower rated/higher degree)
z = rating of doubled bags

This is interesting. And based on my [limited] experience playing combinations with my WM Sequoia, Sycamore, and Everlite, I believe it's pretty valid.

[Tipi Walter]

This is how we all stayed out in the cold when we didn't have much money---crawl inside a cheap fiberfill bag and zip up tight and then throw over an old Army feather bag. We stayed warm and alive though at the cost of Weight and Bulk.

[Sarcasm the elf]

Enlightened Equipment has a pretty good article about doubling up their quilts, sleeping bags work similary well.

https://support.enlightenedequipment...b-zero-camping

[Ethesis]

I have used a 40* quilt laid over the top of my 10* bag to increase warmth before and it worked great. I was toasty warm in temps somewhere between -5 and 0.

That is what I’ve seen recommended far more than a bag in a bag for warmth and lightweight.

[Feral Bill]

When I did a lot of serious winter backpacking (Adirondacks and Whites) this was my standard method. There was a lot of bulk, but I slept well down to -35 F. It's a versatile system, too. These days I'd go with a quilt over bag, I think.

[MacBrave]

x -(70 – y)/2 = z
x = first bag (higher rated/lower degree)
y = second bag (lower rated/higher degree)
z = rating of doubled bags

I have a 20 degree down quilt and a 20 degree synthetic bag. So the equation would be:


20 -(70 – 20)/2 = -5?

I've tried this system a couple times now on boy scout trips with temps down to about 20, and have been toasty warm. Of course that also includes wearing appropriate cold weather clothing for sleeping, and having a good pads or pads to insulate you from the ground.

[Tipi Walter]

I have a 20 degree down quilt and a 20 degree synthetic bag. So the equation would be:


20 -(70 – 20)/2 = -5?

I've tried this system a couple times now on boy scout trips with temps down to about 20, and have been toasty warm. Of course that also includes wearing appropriate cold weather clothing for sleeping, and having a good pads or pads to insulate you from the ground.

We never used any kind of equation---we either just bought the highest quality down bag we could afford (in 1980---a North Face Ibex rated to -10F for $320)---or we used a 5F rated polarguard bag and tossed another cheap bag over it. The Equation worked out like this: Was it enough to keep us warm every night??? Yes or No.

The best way to solve this math problem is to sleep out every night in the winter---either in the backyard or out on the deck or porch or in a wall tent or yurt or tipi or out on a backpacking trip---and Voila! You'll find what works real quick.

[soumodeler]

x -(70 – y)/2 = z
x = first bag (higher rated/lower degree)
y = second bag (lower rated/higher degree)
z = rating of doubled bags

Thanks for the formula. When applied to my 10* bag and 40* quilt I get -5*, which is about what temp I used this combo in, and was overly warm.