My silk underwear didn't have much longevity, though it was comfortable. Liner? I've tried non-silk ones and though I was well cocooned I did not emerge as a butterfly. Actually I felt more like a trapped, rabid wolverine trying to get out in the middle of the night to keep my bag dry! Getting back in is another story with a bad ending. I've gone to my puffy (which generally is relegated to "clean" use around camp and in the tent, and some light fleece pants. I'd much rather use a military poncho liner or a fleece blanket as an extender. They absolutely kick up the rating 10 degrees.