Minimum Required R Value for Snow Camping

What does "thermally neutral" mean?

There's the plot of clo vs temperature that Richard posted http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/9378/index.html

Given the amount of heat produced by a human body, you need a particular insulation value to keep your core temperature at 98.6 degrees F

Thanks for the response Jerry. Basically, thermally neutral means very little heat from my body is going to the snow beneath me, and very little cold is felt by my body from the snow.

Essentially, what does it take for me not to feel the cold beneath me when camping on snow at freezing temps?

The estimates and data I've seen seem all over the map, let alone personal experience. I know lots of climbers who only use a foam pad during the late spring/early fall, even on snow/glaciers. Steve House only brought a Thermarest ProLite 3 on his ascent of the Rupal Face on Nanga Parbat, though admittedly he slept cold. Not using that as a real example, just to say that high up on an 8,000m peak, some people's sleep systems have no more than 3-4 R value.

Hi Sean

Your question does not make a lot of sense, which is why you may have been getting different answers.

Snow can have any temperature below freezing it wants. It can be at 0 C (32 F), or it can be at -40 C (-40 F). You will need different amounts of insulation for these different conditions.

Cheers

Thank you Roger, I didn't know that! I'm not surprised by that fact, but I am surprised I didn't know that. :)

So then, for snow/ice that is approximately freezing (0C or 32F), what is the required R value for a pad?

And similarly, for snow/ice that is approximately -17C or 0F, what is the required R value for a pad?

Thanks,
Sean

An awful lot of people seem to have been happy with a total r-value around 5. The classic combination is a ridgerest (2.6) and an old thermarest ultralite (around 2.2).

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Anecdotal evidence: with a pad that has an r-value >5, I've not been cold on the snow in temps down to the low teens with appropriate clothing and bag. Though, I have other issues in winter (too much moisture). I think if you keep the r-value upwards of 5, you should be ok provided you're not getting into extreme temps.