FWIW I responded mostly with a group or bulk buy in mind, since DavidEnoch mentioned a 10 for $20 purchase option. As I think Mr. Ritter's current advise still recommends, or did last I read it, the mylar blanket is better than nothing, and might be serviceable for a solo or small group survival situation, though mostly in non-blanket / non-personal applications - like building a shelter from rain and snow. But even that requires alot of care with mylar, it will rip pretty easily. I carried a 99 cent space blanket in my bag for backpacking bivouacs for probably 25 years, before AMK began to refine the design and introduced better versions and materials. I never had to use the space blanket though, but I have used the AMKY bivvy in a real night outdoors (backyard) and it held up as advertised. (I still will at times carry a Tacoma Mountain Rescue tent in my bag, which is structurally not much more than a large orange plastic bag to sleep in, if I'm not already carrying another shelter option - its better than nothing). In terms of personal comfort in the great outdoors, $12 for the AMK bivvy is a no brainer versus $1-2 for the mylar blanket. I would have a hard time outfitting a hundred cold shivering people with 100 AMK bivvys after an earthquake though, so if I hadn't done my job and cached some survival tents, if there was a box of space blankets split open in the road, I wouldn't turn them down. Better than nothing, its just a question of how much better.