The old "Space Blanket" has been a staple of survival kits for at least several decades, but do you folks find them useful? Or at least do you find them useful as an actual blanket? Over the years I've tried many different brands and types. For the TL;DR crowd I'll skip to the end!
No, they don't work super well as blankets. I will go into a bit more detail.
Not all "space blankets" are created equal. The very cheapest are usually just a buck or two, and as blankets I have found them wanting. They're very very noise, cracking and creaking with every gust of wind or body movement. And of course the entire premise of them is somewhat flawed. They generally claim to "reflect 90% of your body's radiant heat" back to you, which sounds great. But radiant heat isn't really a big source of heat loss. In actual situations you'll lose most of your heat through convection and conduction. Needless to say a 1 micron bit of mylar won't do much to stop heat loss through conduction to the ground. It does help a bit with heat loss through convection by blocking the wind.
On that score I have found the Titan brand to be a bit better and the AMK Heat Sheets to be about the best. Both of them are much thicker and a lot quieter. They don't do an immense amount to keep you warm but they help somewhat.
If space blankets don't work that well as blankets, are they worth having at all? My answer in an emphatic YES! I think they have many uses. Some of my uses are as follows:
1) Fire tinder- Space blankets are extraordinarily flammable! Crump up about a square food of one in a Sierra cup and hit it with a firesteel and you'll have quite a blazing fire.
2) Rain fly- A space blanket does a very good job of sheltering from rain and to a degree, from wind.
3) Reflector- The mylar blanket does work well in conjunction with clear plastic to make a 'Super Shelter'. It also works great to protect you from the sun. It doesn't offer 100% shade but it blocks/reflects most of the sun's radiation. THIS is the kind of reflected heat that you really can affect with a space blanket! On a related note they work pretty well to cover the outside of your tent. Sometimes I'll rig one on the east facing side of my tent so buy me an extra hour of bearable sleep before the tent gets too warm.
4) Tick batting- A mylar blanket can make a decent improvised tick batting; just wrap pine boughs in the blanket. It will keep them together as an improvised sleeping matt while offering some protection from insects and adding a bit of warmth. It's also a bonus if you're forced to sleep on wet ground.
5) Water collection- I haven't used one for this as a primary function but accidentally I've collected water in space blankets that I had set aside after a use. They're waterproof and pretty strong, suitable for use in improvising a water transport (although they're thin enough I don't expect one to last for a long time- probably days, not weeks).
Most of them time I'll have at least two of these blankets on me, and sometimes a few. I like that they're cheap, light and compact. They're not miraculous and they won't replace a real sleeping bag but I still find them useful bits of gear for my kits.
