I like to see people test their gear in a safe situation first.
If you are going to do an overnight attempt I suggest to people that they try it in the backyard first.
If it does go wrong and you find yourself freezing to death, being able to stop the experiment and go warm up sure helps.

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"

Dousing yourself with a hose will put you at a disadvantage in any scenario Canoedogs - if you don't have available dry clothing you may be relegating yourself to either starting a fire for warmth (iffy and may be alot of work around here in the PNW, depending on season), or a long night of walking and wakefulness, using up your energy to keep warm. I know one hiker who fell into Thompson Lake one day and spent the next 24 hours awake and keeping warm. He was lucky, he knew the trail home and started out by moonlight around 2am, but before that he had spent about 6 hours walking in a circle to stay warm. By the time he hit the trailhead he had pretty much dried out except for his socks and boots, and he had blisters. Ultralighter, once - the guy never left for a hike without a change of clothes again.

Personally I would ditch any foil type blanket in a survival kit and replace it with either a Montane Featherlite or Jetsteam. They only take up marginally more space and weight than a foil type blanket.

Each to his own, and clothing + gear appropriate for the season. With the possible exception of the warmest summer days I never hike anywhere without my "technical" wind+waterproof jacket (similar to goretex mountaineer-type jackets, except the menbrane is not from goretex). Technical hood (i.e. one that works in foul weather), complete water proof, somewhat breathable and lots of ventilation zippers.


I also bring my bivy bag, which weighs 600 grams. Now 600 grams is a lot for the ultralight experts... but unlike "space blankets" my bivy bag is sturdy enough to be used on a regular basis. Most of the time, I unzip and unfold it into a rectangular sheet that I use as a wind break, rain tarp or heat reflector, using the pre-made rope rivets and para chord. Making lunch breaks comfortable is one of the true joys of hiking in a harsh climate... If it's very cold I unzip a ventilation opening and enjoy lunch inside my own micro climate. The bivy bag is even spacious enough that I can add my own heat source, such as a candle or a stove.


While space blankets is better than nothing, using it effectively requires a lot of practice - to the point that tossing a space blanket into your pack will be useless if you haven't practiced with it. You need to destroy a few to experience what works and what doesn't work. Also realize that wrapping a blanket is seeking a goal which is perfected in the shape of - A BAG! Why people don't use "space bags" instead of "space blankets" is certainly beyond me. A bag can be converted into a blanket with a knife in 15 seconds. Wrapping a blanket into a bag is next to impossible....Which is exactly why many survival manuals advise to bring some big plastic bags to make emergency ponchos / bivy bags.

Now uninsulated bivy bags are cold - but they are much warmer than nothing because you're now in a water proof and wind proof container. But even wind+waterproof, you still need to add insulation, both to the ground and between you and that cold bag material. Could anyone please invent some inflatable bubble wrap material that weighs and compress into next to nothing?

Another problem with non-breathing bags is that you will get condensation on the inside. Most likely, your clothes will get wet, or at least damp. Yet another reason to wear wool...

The one survival experience with the older foil type blankets left me worse off than without-I was young, and didnt understand the mechanics of heat generation, and put the foil blanket around me, then a fleece blanket over that. I dozed off, only to wake up later to condensation that had frozen to the blanket. Not a really pleasant experience...
I have an AMK bivy bag, and, should it be used, I think I would stuff leaves, pine branches, or something else in there, to give some insulation. The heat sheets I could wrap up temporarily till I get a fire going, then build a shelter from there...and use it to reflect heat.