what do I get if I add, for example, a 40° quilt or bag on top of 20° quilt or bag?
or a 40° on a 40°
etc...
I know, I know....tons of variables, very personal experience kind of things, which sleep pad, is it wet, etc....
Lets say we are limiting the discussion to non arctic and non alpine conditions, sleep pad that would be ok for the ultimate temps, etc...
but generally speaking
is there any sort of widely accepted rule of thumb equation to loosely predict what I might expect?
as in like maybe take half of the second quilts rating off the base layer's rating, just as an example....
Do you think I might expect comfort down to a ballpark of 20° with two 40° quilts?