Dec 21, 2010 at 1:10 am #1266792
@derekoakLocale: North of England
This is really about physics. We all know that a thin sleeping bag and a mat like a neoair will do in summer but if you are sleeping on snow you need more insulation above and below you say an exped 7. What if it gets colder than just freezing say -20C. You clearly need an even thicker sleeping bag do you need a foam mat under your exped 7 as well?
It struck me that if you are sleeping on snow. Snow is a good insulator as long as you keep it below freezing. Perhaps experiments could be conducted to show that a mat with say an R value of 6 kept your warmth from melting the snow beneath you. Once that has happpened the snow will help insulate you. As the temperature gets colder around you the snow is even less likely to melt and no more insulation would be needed below you.Dec 21, 2010 at 3:32 am #1676295
@jamesdmarcoLocale: Finger Lakes
A lot of people will tell you it doesn't matter. Once you reach an ~R6,no more needed, citing your logic. Well done, BTW.
What about mountains? Not enough snow sometimes to make this work. What about forest duff that gets soaked before freezing? Frozen duff makes poor bedding. 2" of granular ice pellets is not snow. So, there are a lot of conditions out there that want more than R5-6. In snow, it insulates well and the problem is keeping it from melting, R5-6 is fine for a general starting point. Depends on the type of snow. I believe the Inuit have about 20 names for the various types. A lot will depend on the type and composition for the first couple feet. Blown sand in winter is very cold. Far worse than snow for insulating. R6 will not really do it to keep you warm. Sleeping on ice is also bad. This doesn't insulate you all that well.
This is something that it will take some skill and thought. You will need to develope a technique that works for where you want to go and the conditions you expect. But, your logic is sound for a starting point.Dec 21, 2010 at 4:32 am #1676304
@derekoakLocale: North of England
I think you are right my logic only applies to snow.Dec 21, 2010 at 9:15 am #1676366
I took a base-camping winter trip with a girlfriend once when we were expecting temps well below 0*F. She got my subzero bag, I used my 0*F bag. Temps bottomed out around -10 to -15*F that night, & I slept plenty warm. Although my bag was "inadequate," my sleeping pad arrangement was "overkill." I used an Exped Downmat 9… and a Ridge Rest, combined total around R-10. No cold-seep through that pad combo!
My experience has been that it's never a bad idea to have more insulation underneath you. What you might investigate, though, is the most weight-efficient way to do that. In other words, a downmat 9 is R-8 vs R-6 of the downmat 7, and the downmat 9 only weighs 4 ounces more. To achieve the same R-8 w/a downmat 7, you'd have to add a ~14oz ccf pad (ie, std ridge rest).Dec 21, 2010 at 12:44 pm #1676446
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
On snow it does not matter so much. Snow is fairly fluffy stuff with lowish heat capacity. Some heat will leak through the mat from you, and this will warm up the snow a bit. It can get quite comfortable as the snow adapts slightly to your hip shape.
However, as others have pointed out, when you are on solid ice or something with more heat capacity (or 'cold capacity' if you wish), then this does not work so well. Try frozen concrete!
We find that an R-value of over 6 is usually enough – on snow. At this point the mat is usually fairly thick, which is also fairly comfortable.
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