When you hear the phrase “emergency blanket,” those shiny Mylar blankets probably come to mind. Mylar is a shiny film made by bonding vaporized aluminum to polyester in a vacuum chamber. It’s lightweight, and Mylar blankets are sometimes compact enough to fit into your pocket. They’re also one of the most inexpensive kinds of emergency blankets. They work by trapping and reflecting heat, though they may not retain it well in some circumstances. They’re also non-porous, and as such moisture wicking is seriously lacking. If you’re looking for an emergency blanket that’s inexpensive, super compact, and gets the job done, Mylar is a good place to start. They’re often used in shelters during natural disasters and were initially developed by NASA for space missions.