I've made cozies out of reflectix and love it. My standard cold weather setup has
been a sandwitch of two wallmart ccf's with a thermarest in between. I'm nice and toasty
down into the -25C range with that, but it's pretty heavy. I can strap the ccf's to the outside
of an 80litre pack, but it's usually toboggan gear.

Thinking about refelectix, however, it might be worth my while to try some reflectix for the bottom layer. Mind you ccf is pretty light (if bulky) too. Not sure how mugh weight i'd save.

Anyway, I do pretty well with a ccf sandwitch with an inflatable in the middle.