I've only direct experience with the Thermo lite, which is tougher than anything mylar, but not indestructible.

I really want to get a Land Shark and give it a going over. Sight unseen, my guess is it is about as tough a survival bag as your ever gonna come across in this day and age. I may just order one after Christmas. I'm thinking it must be of the same constituency as those HD survival blankets they sell for $12 to $15. If so, they will be bulkier than the Thermo lite, but pretty darned rugged.