having spent a cold afternoon wrapped up like a tightly rolled taco in an "All Weather Emergency Blanket", with both ends exposed a bit, i grew tired of the wind whistling thought from my feet to head. no matter how i tried to tuck it in around my legs, the problem persisted.

that was when i decided a bivi with only a single opening made a better survival shelter for me.

but i still keep a few of those grommeted mesh-reinforced laminated mylar sheets around for make-shift tarps, or as a ground cloth, or as a loaner, or in the vehicle for back-up, or tucked in a small saddle bag, or to use a red one as a signal flag/indicator.