Foam under or over

[HooKooDooKu]

Wouldn't it make most sense to lay directly on whichever has the highest R value? Highest R value on top, lowest R value on bottom.

No, because R-value is cumulative.

However, there are three forms of heat transfer: Convection, conduction, and radiation.
R-value is only a measure of resistance to conduction.

But how warm you feel is going to be based on how the pads handle all three forms of heat transfer.

So while I don't KNOW why some are claiming a CCF pad on top of an air pad feels warmer than the other way around, I see that as a possibility if the CCF pad does a better job at reflecting radiated heat than the air pad. All other things being equal, having the pad that best reflects radiated heat closer to your body would make sense as the arrangement that keeps you warmer.

But there's all sorts of things that might be coming into play. Air that can move is a poor insulator... and from what I've seen of the neo air, the baffles are open from side to side. In other words, a neo air likely has two R-values associated with it... one for how well it resists the transfer of heat from the ground to your body, and another R-value for how well it resists the transfer of heat from the air surrounding the sides of the pad to your body. It's quite possible that a CCF pad does a much better job as resisting heat transfer from the surrounding air, and therefore having a CCF pad on top of an air pad will insulate you to some degree from the side-ways heat transfer of the air pad.

So you really need to know more than just R-value to know how a pad is going to work for you... and every pad is going to be different as it relates to conduction, convection, and radiation.

Since every type of pad in a manufacturer's lineup is going to react to these three modes of heat transfer differently, and those modes are affected by your setup (hammock, ground, tent, tarp, etc)... the only real answer that can be given is that each person simply must try both ways and see what works better for them in there conditions.

[Kaptainkriz]

Indeed, and may even have a little snow on the ground. Looking forward to having fun.

Excellent opportunity to test it in the next 4 days.

[Kaptainkriz]

Well, it was somewhere around 9F last night just South of Manassas Gap. I tented at the Jim and Molly Denton Shelter. I had a Z-Light and an XTherm under a barely adequate Cosmic 21 Down bag. It was definitely warmer with the foam on top and the air on the bottom. That configuration did lead to a lot of sliding but was warm provided I wore a couple layers and a hat. One thing that also contributed to warmness was a Sea to Summit Aeros Pillow. The pillow really helped to keep my head toasty warm. I had not over-nighted in temps that low before. Stuff I learned: My hands froze quickly while setting up the tent and cooking outside. Mittens and a Zippo hand warmer made for quick recovery. I'm glad I took I think Tipi's advice and filled my pots with water the night before. Everything in the tent not with me in the bag was frozen solid. Pot was ready to cook in the AM. The copper strip trick enabled my canister stove to perform very well. The metal toilet seat at this shelter is a cruel hoax!
IMG_3727.JPGIMG_3770.PNGIMG_3773.PNG

[Venchka]

Interesting. Night before last I was in my tent in the backyard and the temperature dropped to 12 in the wee hours of the morning. Xtherm Large and WM 20 degree Alpinlite Long. Once I got through experimenting with various bits of clothing I slept well.
Obviously the Cosmic bag is rated better than advertised or you are a very warm sleeper. Either way it's good.
Wayne


Sent from my iPhone using Tapatalk

[rocketsocks]

Well, it was somewhere around 9F last night just South of Manassas Gap. I tented at the Jim and Molly Denton Shelter. I had a Z-Light and an XTherm under a barely adequate Cosmic 21 Down bag. It was definitely warmer with the foam on top and the air on the bottom. That configuration did lead to a lot of sliding but was warm provided I wore a couple layers and a hat. One thing that also contributed to warmness was a Sea to Summit Aeros Pillow. The pillow really helped to keep my head toasty warm. I had not over-nighted in temps that low before. Stuff I learned: My hands froze quickly while setting up the tent and cooking outside. Mittens and a Zippo hand warmer made for quick recovery. I'm glad I took I think Tipi's advice and filled my pots with water the night before. Everything in the tent not with me in the bag was frozen solid. Pot was ready to cook in the AM. The copper strip trick enabled my canister stove to perform very well. The metal toilet seat at this shelter is a cruel hoax!
IMG_3727.JPGIMG_3770.PNGIMG_3773.PNG

i guess I missed it, but what is "the copper strip tip"?

[Kaptainkriz]

This one: http://www.whiteblaze.net/forum/show...a-cannister-go!

i guess I missed it, but what is "the copper strip tip"?

[Engine]

Spent the night outside on Saturday and used my normal setup with a 1/8" GG pad on the bottom, the Nemo insulated mummy Tensor inflatable, and my EE 20* quilt. It only got down to 29* and I had to stick an arm outside the quilt a couple times to shed some excess heat.

In the morning, after being outside of the tent for about 90 minutes I went back to pack it all up. By then the top of the inflatable felt pretty chilly to the touch, but when I put my hand between the pads I was surprised by how warm it still was there, especially compared to the floor of the tent which was quite cold. It's amazing to me that just 1/8" of evazote can provide that level of extra insulation.

[Rightfoot]

Had a great weekend other having to depend on a rolling start to get the old diesel truck to start Sunday morning... It was down to 9 degrees Friday and 5 degrees Saturday night, both nights with a light breeze. I went foam on bottom the first night and slept well. The second night was foam on top and I believe I slept even warmer. The major problem with foam on top was staying on top of the pad without sliding off although this can be fixed with a little creativity. Thanks for all of the ideas, especially to Tipi for the water in the pot idea. As Kaptainkirz said above it worked great.