As stated before, you should know how to use these for them to be effective. I would also use these as an outer layer to a sleeping bag or blanket as opposed to a base layer if I used it for that purpose. During a military survival course I found other effective uses for them which I now prefer as opposed to using them as a sleeping bag etc. See below for other uses. 1. Lined the inside of my shelter which prevented heat from escaping as much as well as waterproofing my shelter killing 2 birds with 1 stone. ***be careful when puncturing these, once a hole or tear starts it will continue. Good ol duck tape solves that problem for me. 2. Placed a couple branches (vertically) about 1ft behind my fire and attached the emergency blanket to it so that it would continuously reflect heat from the fire into my little shelter that was also lined with an emergency blanket. Be sure not to place it to close to the fire as embers will burn holes in it. It will still work but wont be reusable if you plan onit moving or using it for something else. Talk about staying relatively warm. The temperature was 6-8 degrees by the way. 3. These are amazing signaling devices. It acts like a ridiculously oversized mirror and is highly contrasting to the environment and highly visible. All good things when trying to get found.