To keep my face warm I use either a balaclava (homemade of poly fleece) over a wool cap (I use a quilt, so I have no sleeping bag hood) or if it is not so cold, a wool buff worn like a hood. I use the 'clava over the cap so the cap does not scoot off my head at night.
I'll have to try a balaclava. My woolen cap kept falling off last night.
I've noticed a lot of folks are using quilts now instead of sleeping bags. What are the advantages?