Does a sleeping bag liner add warmth?

[Poser]

I have the same Thermolite Reactor which I add to my 20 degree quilt once temps get cold in October. I don't believe I've used it before October. I find it makes a pretty good differenace, though I'm hesitant to put a metric on that differance.

 

[RJ_Ruff]

In my experience, liners don’t add nearly as much warmth as the manufacturers claim. I’d agree that 5°F is probably about the upper end in ideal conditions, but most of the benefit I’ve noticed is keeping the bag cleaner and reducing drafts. If I’m expecting colder temps, I’d rather put the weight toward a warmer bag, a higher R-value pad, or wear my puffy layers to bed.

 

[cbuck516]

On one float trip where it got down to below 30F, I had to give my sleeping bag to my wife because she was cold so I slept in just the Reactor liner. It definitely adds warmth but it's not a huge amount. I didn't die, but I got my wife a nice pad and bag after that trip.