I've been carrying a "Blizzard Rescue Blanket" for trips lately, particularly when I am solo in cold weather. The blanket is heavier than the mummy option, but looks easier if I'm dealing with an injured party who has limited movement, and is still just over a pound.
What worries me is the heat loss through the bottom of the blanket. I once used only aluminized mylar blankets below a down bag; but I was much younger then. The documentation for the blizzard rescue blanket doesn't recommend any particular ground insulation.
I've considered carrying a closed-cell foam insert in the back of my pack; I had a friend who carried such an insert, and was able to nap with this small insulator below his butt, leaning back on his pack.
I recall someone posted about two years back, about actually trying this setup for a night.
Any idea? In an emergency, is the natural reflectivity of the blanket enough? Should I augment with a minimal thermal pad as well?