Tyvek is a synthetic material made of high-density polyethylene fibers; the name is a registered trademark of the DuPont Company. It has a number of uses, including envelopes and siding for houses.
Tyvek has been used by the United States Postal Service for some of its Priority Mail and Express Mail packages and for banknotes in some countries.
Tyvek superficially resembles paper; for example, it can be written and printed on. However, Tyvek envelopes may not be recycled as used paper. Instead, DuPont runs a recycling program, at least in the USA.
Tyvek is manufactured in Richmond, Virginia and Luxembourg.