View Full Version : R-value vs. length
I just bought the women's thermarest pro-lite plus, inflated it, went to test it out and my feet and ankles were hanging off the edge. I wanted the women's model because the R-value is 4.5 versus 3.8 for the men's. Is it better to keep the shorter mattress with a higher R-value or exchange it for a longer one, more comfortable? with a lower R-value? I have a 6 ft. 30 degree bag and tend to sleep warm. It may be used for an extended/ thru hike in the future. The men's and women's versions are the same weight.
Can you put whatever you use for a "pillow" off the top end of the pad? That would probably add at least the 6 inches you need to get your feet on the pad. Entirely dependent on what you use for a pillow, and how you like to sleep though.
skinewmexico
05-06-2011, 23:44
Or put your pack (jacket, whatever) under your feet.
LIhikers
05-07-2011, 00:13
Warmer is always nice if you plan to go out in winter as well as the other 3 seasons.
If my feet are not warm, my body is not warm. My feet need to be on a mattress to stay warm. Nothing else works for me as well. I like a full length mattress.
Panzer
I totally agree. I like a full length pad...I cannot do the short pads and making do with other items under my legs. But hey, that's me.
But how about taking along 2 sections of a ZLite and folding them over at the foot (or head) of the pad at night, and of course the ZLite can be used as a sit pad during the day. If making it stay in place is hard, just take along 3 sections and leave onde section under the other pad while the other two are folded over on top of each other...if that makes sense...
If my feet are not warm, my body is not warm. My feet need to be on a mattress to stay warm. Nothing else works for me as well. I like a full length mattress.
Panzer
Agreed.
Thanks for all the suggestions. I sleep on my stomach so either my feet or arm (it always ends up under the pillow) would be on the ground. That just sounds cold and uncomfortable. I'm still not really sure how much 1 R-value is or how that equates to warmth, but I'm sending the women's version back for the men's longer mattress.
Exped is brave enough to give you a suggested minimum temperature alongside its R value.
Around your R values it lists R 3.2 at -5c 23 f
R 4 at -11 12 f
R 4.9 at - 17 1.4f
http://www.exped.com/exped/web/exped_homepage_int.nsf (http://www.exped.com/exped/web/exped_homepage_int.nsf)
BTW, the W version (R4.6) is 66" long as against the M version (R3.8) at 72 ".
So the same weight but warmer and shorter. (as per specs ...)
Franco
"R value" is used to calculate conductive heat loss. In english units it is given in hr ft^2 *f / BTU. So heat loss over time is (Area x Delta T)/R= Heat loss in BTU/hour.
R values can be added together in sequential heat flow to get "total R" so Rclothes + Rsleepingbag + Rpad = Rtotal. Qs (heat loss) cannot be added together in sequential heat flow, as Delta T changes through the system.
There is also such as you're wearing a jacket on 40% of your skin, pants on 40% of your skin, and nothing on 20% of your skin. In this case you can calculate Q (heat loss) for each area and then add them together to get total heat loss.
R value does not take into account either convective or radiated cooling. Convective cooling is why being in a tent or shelter will make you feel warmer, because you are out of the wind. Radiative cooling is why the Ridgerest Sol is warmer than a normal ridgerest despite having the same R value.
you could also have 2 mattress. Use 1 in warm weather and 2 together in cold weather.
Panzer
Jonnycat
05-09-2011, 21:54
you could also have 2 mattress. Use 1 in warm weather and 2 together in cold weather.
Some find success in putting one of those thin blue pads on top of their air mattress for more insulation.