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Six Moon Designs says:
Six Moon Design's Polycro footprint is made from ultra strong and ultra light Polycro membrane. Designed for shrink wrap and frequently used as a second thermal layer for windows, this material is exceedingly rugged. While not as durable as Tyvek, it'll provide significant protection and weighs virtually nothing.
Be careful though, this material is so light, it'll blow away in a light breeze. So be sure to weight it down after you spread it out.
This Footprint comes two per pack. So you've got twice the protection