Ground Heat Solution

Yes, insulation works to limit heat flow in both (either) direction. In your house, the insulation limits heat gain in the summer AND heat loss in the winter.  Thus, a ground pad with a higher R value (larger insulating resistance) will reduce heat transfer between your body and ground going either direction.

Everything Alan said is 100% accurate. An additional consideration is that the X-Therm has reflective properties that bounce your radiant heat back toward you. I cannot sleep on my X-Therm above 40 degrees because I’m uncomfortably hot.  I’m curious how an X-Therm would play out in the desert situation Atif described. Would it be best to flip the X-Therm upside down?

I’ll try the higher R value next time. For reflected radiant body heat, there isn’t much of a solution besides elevating the body for ventilation, which would not be ultralight. I remember going through my grandfather’s WWII gear from when the Allies fought the Japanese in Burma, and there was this curious looking canvas mat with metal attachments used to suspend the bed. It must have weighed about 5 lbs. but it certainly would have addressed both ground and body heat.

A hammock could work, but not practical in most deserts. The only ultralight solution I can think of is sprinkling the body with a small (25 ml) amount of water and allowing the evaporative cooling to do its work. Welcome any other suggestions.

Yeah, the problem would be that while a higher r value mat would insulate you from the ground, it would then also mean that you retain more of your own body heat.

It might be the lesser of two evils, or it might just be that they cancel each other out and you don’t really feel much difference.