It has to be cold my wife doesn't wait for it to be cold she's always lippy, if you don't think so she'll tell ya! LOL!
Psalm 19:1-3 "The heavens declare the glory of God; and the firmament sheweth his handywork. Day unto day uttereth speech, and night unto night sheweth knowledge. There is no speech nor language, where their voice is not heard."
Good thing I didn't make my quilts yet, lol! 2layers for bottom 1 layer for top glad we worked out that kink in the design before I started sewing...er uh uhm I mean operating my power tool!
40 is a good width for minimizing bulk, a few inches more narrow felt a little too narrow. as for length, i like the length from the back of my neck to several inches past my crotch.
the amount of insulation you need also greatly depends on how efficient the design is, any sizeable air gap between the uq and hammock can greatly decrease warmth and efficiency, as will any loft compression or not having a nice tight seal around the edges.