A vapor proof lining -- also called vapor barrier -- inside your sleeping bag has its use, but for most of us it's purely theorethcial. The vapor barrier prevents condensations to accumulate inside the insulation of the sleeping bag. You loose a cup or so of vapor through sweathing each night, and if all of that accumulates for days and weeks then the insulation value gradually drops. Essentially, you get lumps of ice inside all that nice fluffy insulation material. Not good.

Most of us aren't at polar expedititions that lasts weeks, and would rather not deal with the downsides of a vapor barrier: It gets rather clammy and damp.

If your sleeping bag isn't up to it, I've had great success making lining out of army surplus wool blankets. Fould doble and stitch a cocoon with an inch or two wide stitches, it takes 2 minutes, cut away the surplus. Heavy, bulky, but works wonders to augment a sleeping bag.

I haven't tested any of the fleece liners, but I'm sure they're good.

And wool underwear. I'm a big wool fanatic. Modern merino wool is fantastic.