George, thanks for the link. When you get synthetics going I'm interested.
FWIW I ALWAYS sleep in mummy bags with the open zipper below me, using the bag as a quilt. That puts the thickest fill in the wrong place on some bags but I don't ever recall zipping up a mummy totally, even in -40.
I made my first quilt in 1978 with hollofil insulation. Am in the market for a new bag and maybe finally will buy a pro-designed quilt. Buying a mummy to use like a quilt has been easier than my amateur sewing projects.
I suspect that some people would hate sleeping under a quilt. I am the opposite and don't like the confinement of sleeping bags.
My apology for not adding anything to the discussion about selecting a brand.
