down sleeping bag overfills

4:51 p.m. on December 21, 2003 (EST)

are the overfills such as those offered by western mountaineering really necessary? i'm about to purchase a bag, but have reservations about this option;isn't the standard amount of fill in a $500 sleeping bag enough?

5:43 p.m. on January 2, 2004 (EST)
4,404 reviewer rep
6,006 forum posts
Sorry I didn't catch this before --


are the overfills such as those offered by western mountaineering really necessary?

Short answer - no, not really, .... unless ...

Overfill on a bag serves several purposes. If the bag with standard fill is adequate for the conditions you are going to use it for, then overfill is unnecessary. For example, if you are never going to take your 0-degree bag into -10F conditions, buy it as is. But if you are planning to go into -10F conditions from time to time (spending 2 or 3 days at a time, for example, or going into such conditions a couple times a year), then either get a bag rated at -10F or consider overfill of about 2 ounces (typically it is about 5 deg F per ounce of overfill). Overfill is a good buy if the bag you want has features you can't get in a bag of the rating you need, but generally you are better off getting a bag rated at the temperature you need.

My bag for deep winter backcountry and Alaska Range climbing is a Feathered Friends Ptarmigan, normally rated at -20F. Since I regularly encounter -30 to -40 temperatures on these trips, I got 4 ounces of overfill (an extra 20 deg of warmth). I wanted several features of the Ptarmigan over FF's colder weather bag as well. My oldest down bag, an Eddie Bauer Karakoram vintage 1960, also has about 4 ounces of overfill, and was also a -40F bag originally (it has lost a bit of loft and a few down nodules over the years, thanks in part to not catching a tear in the lining quite fast enough - didn't have a needle with me and hadn't learned to use dental floss as a universal repair thread at the time). It is probably a -20 to -25F bag now.

Western, along with Feathered Friends, Marmot, and Integral Designs is conservative with their ratings, as has been pointed out here many times before. Keep in mind that the ratings make assumptions like - you are in an appropriate tent for the conditions, you use an appropriate sleeping pad for insulation, you are properly hydrated and fed plus not exhausted, you wear dry clean sleeping clothes appropriate for the environment (Warmlight - Stephenson's - preaches sleeping bare and supposedly his ratings reflect that, but others assume mid-weight long johns for sub-zero temperatures), and a few other assumptions.

So the questions you have to answer are how cold do you personally sleep, and is the rated temperature of the bag adequate for you and the conditions you will go out camping in?

May 22, 2018
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