Interesting product, and good discussion to be sure. I stumbled across this vest recently (online) and was thinking that while it had to be more insulative than a plain space blanket, the convective losses would steal a lot of heat, especially when you're sitting still. However Benjammin's experiences seem to refute that to a degree.

I agree that you'd be hard pressed to find a fleece vest that weighs this little & packs this small.

Like many things on the market, I wish I could wave a magic wand and make tweaks to what is a reasonably promising design:

- construct it from the same quiet, strong plastic as HeatSheets
- add just a little baffling of some kind to the chambers
- put a little bungy cord/elastic around the arm holes & bottom hem to keep warm air from being pumped out each time you move

Of course, by the time you did all this it would weigh twice as much and cost $30.

Here is the product's webpage & it has some more details. Here is a detailed review from Backpacking Light that I think is freely available without a subscription.