Originally Posted by
Tourist in MSN
A gal that I used to work with always used a sleeping bag liner in her bag, she said she did it to keep her bag cleaner. That made a lot of sense to me, so I started doing that over a decade ago. I have a silk one and a microfleece one, I pick which to bring based on anticipated cool or warm weather. I find that a sleeping bag liner works great in hot weather by itself, and as it cools off during the night I start using more and more of my sleeping bag.
They also add a bit or warmth in cooler weather and can be used without the bag on warm nights. I haven't used mine in a long time though. I decided for me it wasn't worth the extra few ounces since my sleeping bag seems to stay pretty clean.
I do try real hard to avoid sweating in my sleeping bag so that minimizes the need. I do that for two reasons. First sweat isn't that good for the bag or it's cleanliness and second it means you will likely get colder when the temperature drops later and you are damp with sweat. I tend to go in stages as it cools down. Maybe starting out out of the bag, or using it like a quilt, hanging a leg out, and so on, only getting in and zipping up tight as it actually gets cold. I think I stay warmer for the bag's rating by not getting all sweaty early in the night.