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Posted by Bill S on October 21, 2006 at 11:12:41 am EDT
In reply to Re: Feather question posted by Blackbeard on October 21, 2006 at 7:34:42 am EDT

The young man with the Black Beard asked:
"Can anyone explain the broad variation in how some reviews indicate the temperature ratings are so out of kilter? Are some of these bags' ratings just hype, or is it mostly individual dynamics, like metabolism, and under padding, etc.?"

Besides the longer comments,

1. some of the ratings are "optimistic", or in harsher terms, hype. This is true of most of the mass market bags.

2. many of the ratings are based on measuring the loft and using the old USArmy tables, which basically are for survival wearing your combat gear in the bag. They do not account for bag construction - sewn through or not, zipper baffle, neck baffle, tighter-fitting (warmer) vs looser fitting (cooler, with rectangular bags being much less warm for the loft), mummy vs other shapes (the hood keeps warmth in, rectangular has open top which leaks lots of heat).

2a. some of the ratings assume sleeping in a tent, some assume sleeping with nothing on, some assume sleeping with clothes appropriate to the conditions (little for warm weather bags, long johns for cold weather bags), some make assumptions about the thickness of sleeping pad (thicker for colder conditions, so more underneath insulation) - again no consistency from company to company, no industry standards.

3. There is no standard for testing warmth of bags, although within a given company's range of bags, the relative ratings are ok (Company A's 0 deg bag will be warmer than their 30 deg bag, but Company B's 0 deg bag may be warmer or cooler than Company A's 0 deg bag).

4. Individual variations, both person to person and for a given person's current condition, make a big difference - fatigue (more fatigued generally means colder), recent food intake (food eaten just before getting in the bag generally means warmer), exercise (doing a bit of exercise just before getting in the sack generally means warmer), clothes worn in the bag (some people sleep in the buff, some in their long johns, are the clothes damp from sweat or from being out in the rain or snow).

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