That info on the aluminum foil is really interesting Jim. I hadn't thought about why the foil gets hot and the reflective mylar does not, but I know that's the case and now that you've explained why it makes perfect sense.

The real trick to maximizing your warmth with a reflector (aside from choosing a good one) is to arrange it so it reflects the heat at YOU. While this may seem obvious, I think it may be a big part of the reason why people haven't caught on to using them more.

This is why a Baker's Oven style shelter works good. A reflector set up like a flat panel behind you won't do much good at all, but if you set it up with a back and two angled sides and sit in front of it, like so:

    X
\____/

you'll instantly feel the heat reflecting back at you. Those angles are very important. I've tested this a lot. They don't matter near as much when you have a roof and front panel to trap the heat inside, but they make all the difference in the world without those.

When you add a reflecting roof over it and sit inside it you start trapping the heat and really start warming things up, and when you add that clear front wall panel and sit inside where there is little draft the temp inside evens out and everything inside warms up, the ground included. Keep your fire going for a few hours before you go to bed and the ground will help keep you warm inside after the fire has burnt out.

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I'll share a few more thoughts I've had on this subject:

It's occurred to me that using this material in combination with a tent heater would probably allow one to use a heater with less BTU output and maybe even stay warmer at the same time. I haven't tried that yet, but I do wonder how well it might work with even just a few candles burning inside. If you could fashion a safe, lightweight heater and raise the temp inside just 10º that could be pretty significant.

I'm not sure you can make a "Foolproof" tent heater, but you can probably make one that's safe if you don't do something foolish, which is worth looking into. A tent and heater designed specifically to work together might produce a very good result.

Also, think about a bivy style tent with an arched roof that's centered over the sleeping bag. That should direct the reflected heat right onto the sleeping bag. If you designed the angles of the arch correctly it should heat the bag very evenly too. Put a half dome at the foot and head and you get some extra heat in those spots.

There really is a lot of ways to put that material to use that I haven't seen tried yet. Honestly, just sitting outside on a cold night with no fire at all and wrapping one of those SOL blankets around you keeps you a lot warmer.

I carried one of those walmart blankets for probably 5 years and never even took it out of the original package. I think a lot of us have probably done that. Now that I've taken the time to learn and practice using one, I actually use it. The SOL blankets really are a pretty amazing piece of UL gear.