how much r value for snow?

5 under the torso, and more can't hurt.

Rule of Thumb. You need twice as much for winter as you do for summer.

–B.G.–

A couple of centuries ago I used a single full length closed cell foam pad for two weeks climbing Mt. McKinley. R value was probably around 2.

Each time we broke down the tent to move to a higher camp there was a shallow basin melted in the snow under the spot where I had slept.

I had a -40F bag, but slept cool as I recall. Nonetheless I did make the top and did not freeze to death.

Some people sleep warmer than others. But I don't think you want to be melting the snow at night with your body heat. You will have less energy the next day having expended it during the night to stay warm.

I think Bob and David are in the Ball Park at R 4 or 5… depending on the air temp. Some snow is colder when the air temp has been colder for some time.

But, hey, experiment a little to see how warm you sleep. The cheapest experiment would be two full length foam pads at about R2 each = R 4+.

Billy

Billy

Just my very unscientific opinion, but I don't feel that air temperature matters all that much with regards to ground insulation because the heat transfer is largely dominated by the large mass of cold cold snow.

I always heard that 5 is a good minimum. I don't go with less than 6.

air temp most definitely affects snow temp…

snow in colder air temp regions is colder.

besides that, you need to consider all 4 sides of your body..

if the air temp is too cold for the upper 3 sides of you and your sleeping bag… it would be very good to at least have more R value under you…. but if your sleeping bag is overkill warm, then you can get away with a little less R value under you…

I wouldn't recommend slavishly following the 'recommended' R values.. there are a lot of variables… your bag warmth, how warm you sleep, how exhausted you are at the end of the day, air temp, and snow temp, etc…

We always used to use just a single closed cell foam pad in the Sierra (about 2 R value) … maybe we just didn't know any better… but we had fun and no one froze… (though I would recommend more than 2 now)

Billy

Like Billy Ray we used a single full length CCF on snow when we were younger and tougher. As others have said r-5 is the general rule of thumb. When I have done any kind of searches for reviews/opinions I can say that no one ever complained of being cold on the r-5.9 Exped downmat or anything with a higher r value. Even with r-5 I will get some melting of the snow underneath.

I have never needed anything more than the Exped Downmat (5.9r as mentioned above), but I have only been slept in -25C/-13F temps. My next step would be to add a CCF layer beneath it if ever required. I read somewhere on his site that artic explorer Jerry Kobalenko found the exped down mat useless in sub -30C temps (valves not sealing). You can google his name for more info. I can say from experience that an exped down mat, even uninflated, adds noticable r value.

Hope this is helpful.

Derrick

Many of the SAR folk of my acquaintance don't bother worrying about it and take just a CCF. I am of a colder nature and take a Z Rest with a normal 3 season inflatable – usually my BA Q Core, which is advertised as being R value of 5 (15 degrees).

Snow is a lot warmer than concrete, ice, or rock, being mostly air. In a survival situation, you can dig a snow cave (don't forget a ventilation hole) and be alive but uncomfortably safe at around freezing – 32F – for the night regardless of what's going on outside.

On a winter training one snowy weekend, we were put into a garage for the night – I was happily warm with my overkill Downmat 9. I don't typically take it backpacking tho. But it did the trick all by itself on the concrete at 10F.

I agree that 5R is the minimum for winter but the higher the better within reason. Once you sleep on an Exped downmat at 8R you'll wonder why you waited, although these babies can have baffle blowouts at the worse time. I was on Day 1 of a 19 day winter trip last year when my Exped blew out a baffle and so I had to hike 12 miles off the planned route to pick up an emergency Prolite pad cached in the woods, just in case.

Now Exped is outside my Circle of Trust and instead I use an inflatable Thermarest with a backup Ridgerest solar. So, if my Thermy dies I always have my Solar at 3.5R and it's long so I can double it up for my torso and get thick foam at 7R.

I think much of the issue with all down mats is how much the person's body sinks into the mat. That seems to be mostly a factor of body weight, weight distribution, and inflation pressure. If a portion of the body sinks significantly, then the insulation at those points is reduced.

With the Exped Pump models (with the integrated pump), it's difficult to get these inflated firmly because the pump section of the mat uses any air which would otherwise keep the mat more firm. The resolution of this is to use an inflator (ugh, defeating the purpose of having an integrated pump).

I always bring an 18 x 18 x 1/4 inch CCF square to sit on in the winter, and I use this as a hip/torso pad on top of the Downmat. That works fine down to about 0 to 10F. Lower than 0F (-17.8C), I always plan to bring at least a torso-sized Ridgerest (R-value 2.6).

Jerry Kobalenko reports that the valves were impossible to open at -30C (even with pliers). (http://kobalenko.com/geararchives2012.htm) I remember having a minor issue with the valves, but a brief warming with body heat made them usable again. It could be that my mat had not cooled to the air temperature though.

I slept on my Exped Downmat 7 Pump model (R-value 5.9) at about -15F (-26C) for a few hours in the backyard this past winter inside a double wall tent (Scarp 2 with solid inner). This was on about 6 inches of packed snow. I needed a Ridgerest CCF pad under my torso and on top of the mat to prevent the mat from feeling cold.

"In a survival situation, you can dig a snow cave (don't forget a ventilation hole) and be alive but uncomfortably safe at around freezing – 32F – for the night regardless of what's going on outside. "

That assumes:
1) The snow is deep enough for a cave.
2) The snow is not too soft to create a cave or too hard to dig
3) that you have something to dig with
4) That you have waterproof clothing head to foot to keep you dry while digging
(you can get soaked with all that snow falling on you and melting on your cloths)
5) That you either know how to dig a snow cave or are skilled enough to learn quickly
(it's not hard to figure out, but believe me some people are not very handy at things)
6) that you dig the snow cave before you become so chilled that you can't perform.

I figure you know all this Lori, but we must remember that there are total Newbies on at BPL who could take your comments and go out into the snow without knowing any of the above expecting that in a pinch they could build a snow cave…

Billy

Does anyone use the combination of: CCF + Klymt Inertia + bag?

If one is bringing a bag instead of a quilt that seems, in theory, like a good way to get more warmth for the weight.