Sleeping pads for cold weather

[fern]

quote:

---

Originally posted by pope:

Seems I once read that closed-cell foam is always warmer since what really counts is "dead air", not thickness. Open-cell inflatables (like the Therma-Rest) supposedly allow for little internal air currents which conduct heat away from you. It's kind of like a double-pane storm window. One might think that a bigger gap between panes would provide more insulation, but in reality, the warmth of the inner pane causes adjacent air (or some kind of gas) between the panes to rise, while the cool outer pane cools the adjacent air, causing it to fall. When the gap between panes is thick enough, a current sets up in which air on the warm side of the gap rises to the top and then shifts to the cold side and falls into the cold side of the gap (replacing the cold air that falls down). The falling cold-side air eventually shifts to the warm side to replace the rising warm air. Of course, this circulation takes warmth away from the inner pane and transfers it to the exterior of the home. Storm windows are actually designed with a very narrow gap between panes to discourage these little "heat-pump" currents.

---

A thermarest is nothing like a storm window. When you are lying on a thermarest the warm side (you) is on top, the cold side (snow) is on the bottom. Warm air rises, so the dead air inside thermarest that you warm up stays at the top, the cold air stays at the bottom and there is no density driven heat pump. The only convection you might get is if you shift around a lot and mix up the air inside, but it's still always going to be warmer than ambient.

[rayborbon]

Hey Fern wassup!