some years ago i tested the foil blanket out at my cabin.on a cool,wet day like i might find on a spring or fall canoe trip i wet myself down with the outside hose,went off into the woods a bit and wrapped up in a good quality foil blanket,not the 99 cent ones you find around that you can just about see thru.anyway it did not take long to find out that one-they are not magic,if your wet they will not reflect enough heat to warm you up. two-your head gets very cold. three-they don't cover very well,grabbing the sides and pulling them around you still leaves air gaps.as a last part of the test i took off my shirt,i was really cold by this time,to see if it worked better next to bare skin.nope--it was like having cold wet plastic plastered across your back.i got back inside and warmed up in a hot shower..this was sort of a rushed"lets see if it works" test that lead me to make sure i had some sort of sure fire,fire making gear in my PFD and now i'm looking for a small stove to fill that need.if i did this test again i would have my wife film it for Youtube,try with dry clothes or just damp and not drenched.try a foil bag and not blanket.maybe waste a Heat sheet as a test.as a result of this the foil blanket in my Ditch Vest would only be used as a waterproof cover for a shelter.some things i thought about later were that maybe rather than just hunker down i should have walked around or just hopped up and down to make more body heat or made the blanket into a poncho by cutting a small slit on top and using my belt around it to hold it closed and work at fire making or shelter building with the foil poncho on and see if working at that warmed me up at all..anyway..before you test think about it and everything you might want to try and don't do what i did which was just run outside cold and wet it "see if it works"