I keep one of the cheap foil space sleeping bags in my pack, never used it. I have used a regular space blanket, noisy and reminded me of the tin man of Oz!
The Ptarmigan Bivy weighs only 6oz, might be a good idea to stuff one of these in a daypack for emergency use. A pard uses one under a tarp shelter as part of his sleep/shelter system and says it works well with his 30deg WM down bag.
