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Posted by Bill S on December 9, 2007 at 1:18:33 pm EST
In reply to Sleeping bag liner posted by Spion on December 7, 2007 at 11:56:29 pm EST

calamity's mention of atmospheric conditions reminded me of one thing I didn't mention - humidity. Waterproof-breathable outer shells, whether your parka or the shell of your sleeping bag (or the tent, for that matter) depend on a gradient of both temperature or humidity to work properly. Same is true of microfiber shells on your sleeping bag. High humidity, and you get condensation and/or frost in huge quantities. Low humidity, and the vapor just goes on out - faster with microfiber than wp/b. As long as you are in a tent, you are better off with a microfiber shell than with goretex, DriLoft, or even eVent. The good microfiber (like Pertex) will shed spills reasonably well, if you wipe them up fairly quickly, and the tent should keep the rain or snow out.

But high humidity and lack of ventilation will allow the tent to create rain and snowstorms inside (another reason not to cook in the tent, along with the carbon monoxide, oxygen depletion and fire hazard problems). One of the big problems we often have in the Sierra, where the temperature is just below freezing, is wet snow, high humidity during one of the typical maritime storms (Cascades has this, too, and the BC coast ranges), and the resulting lots of condensation in the tent, since all your gear is wet on the outside as you climb into the tent. Dragging all that water into the tent makes it hard to keep anything dry. Sometimes a bivy sack over the sleeping bag helps (except for the condensation inside the bivy). It's so much nicer at altitude in the Alaska Range or Rockies where you have dry air (and light, fluffy powder to ski in - note I said "ski in", not "ski on", none of this hard pack nonsense we usually get in the Sierra and you always see at resorts). It's cold enough that nothing gets wet, and properly ventilated tents don't develop any condensation or frost.

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• Re: Sleeping bag liner - calamity 01:39:08 12/11/2007

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