Plastic / Tyvek Envelopes (Non-Padded) Put in Garbage Cart Tyvek Envelopes are Plastic, Not Paper Tyvek is a synthetic plastic material.In addition to Priority and Express Mail envelopes, Tyvek is used to make wristbands for concerts, race numbers, CD sleeves, house wrap and protective suits. Did You Know? Express Delivery = Higher Impact Having things delivered express has a higher environmental impact than shipping them more slowly. Items shipped overnight are often packed with extra materials, like bleached paper, that usually aren’t reusable. And because of the high CO2 emissions of airplanes, ground shipping is generally the greener choice over air shipping.