Tyvek is a brand of flashspun high-density polyethylene fibers, a synthetic material. The material is very strong; it is difficult to tear but can easily be cut with scissors or any other sharp object. Water vapor can pass through Tyvek, but not liquid water, so the material lends itself to a variety of applications: medical packaging, envelopes, car covers, air and water intrusion barriers (housewrap) under house siding, labels, wristbands, mycology, and graphics. Tyvek is sometimes erroneously referred to as "Tyvex."