How much wear and tear occurs to a sleeping bag on a trip up Denali? Or, put another way: How many trips up Denali can you expect to get out of the same sleeping bag?

I ask because I would like to loan my almost new Western Mountaineering Puma MF (-25 rating, down, micro fiber shell) to a friend for a Denali bid. However, we're both worried about what 20+ days of continuous use will do to it. People talk about getting many seasons out of a bag, but that doesn't help me unless I know how much they used it during each season. I'd appreciate any information how many days of use I can expect out of a bag. Thanks.

Wear and tear during a Denali expedition on sleeping bags is quite light. You will be sleeping in most of your clothes and inside a tent. Don't spill anything on it and it should be just fine. I have over 1,000 nights in my WM Apache Super Dryloft bag, and except for a small tear from sleeping on a rock ledge, is still going strong. I have a FF expedition bag and happily loan it out, knowing that it will get used like it should.

You must really like your buddy
20 days in a bag even on Denali makes the bag smell like the last one using it.
You'll want to have it cleaned when it returns. Cleaning will generally shorten the life of the bag unless the cleaner REALLY knows what they are doing. I have a Trailwise Chevron bag that is still "like new". It finally REQUIRED cleaning and has been cleaned once by Feathered Friends a couple of years ago. Its first Alaska trip was in 1976.

Stove fires, camp fires, animals, crampons, open bivies and body oils/odors are the few things that will actually destroy a bag.