The ultra light weight tent and sleeping bag bivy is constructed using a mylar type material with a tear and puncture resistant coating. They are durable enough for repeated use, so they can be folded up and put back in the waterproof nylon stuff sack. These can be conveniently clipped onto gear for transport and are compact enough to be put in a car glove box. These are helpful in a car accident or unexpected breakdown. ECO-FRIENDLY – Proprietary Aluminized Polyolefin Sleeping Bags.