Polyester / Mylar

Mylar is a brand-name (from DuPont) for polyester film.  Poylester has fast replaced acetate (a wood-pulp product) for the graphic industry.  Acetate yellows and becomes brittle with age whereas polyester (a petroleum product) is acid-free, optically clear and will not deteriorate with age.  Drafting film (also known as "frosted") is a polyester film that has been made translucent and given a matte surface to allow the use of a pencil.