I don't have much personal experience with the thin aluminum mylar ones. The ones we use to have here at EMS where aluminized 'reflector' on one side and a 'plastic' backing on the other.... don't remember the company. As someone said, it didn't pack as small as the mylar one (don't know if we are talking about the same one) but this one was decent. While not very 'insulatory' I can tell you it worked. Had a mild to moderately hypothermic and soaking wet patient (who refused to take off the wet clothes) actually stop shivering within 5 min of wrapping him up with it. It did a nice job of reflecting his body heat back to him even though he was soaking wet.