Refletix reflecting bubble roll, cut to torso size, reflecting side facing your body, secure with velcro, over the shirt under the jacket, works better than the best winter jacket, a roll costs $9, one roll can be cut for three average size people. Good idea to keep in the car during winter trips. Available at most hardware stores.
Interesting material. Never used it. I have a chicken coop that could use some.
We insulate our chicken coops with this stuff.
Works extremely well.