I've used the mylar sheets with a blanket (on top) and it did help, but the NOISE kept me awake.
I've not tested it, but I carry them in the car. Since they do reflect heat, I'm thinking they would help contain body heat if a person(s) had to spend time in their car in the cold. Roll the edge in the top of the windows, and tape them in place with duct tape.
Has anyone ever done this?
Sue