Historically there have been three major types of film base in use: cellulose nitrate, cellulose acetate (cellulose diacetate, cellulose acetate propiarate, cellulose acetate butyrate, and cellulose triacetate), and polyester (sometimes called Estar).
<Context ref.>Film base - Wikipedia, the free encyclopedia. [En línia]. [Consulta: 6 juny 2006]. Disponible a: <http://en.wikipedia.org/wiki/Film_base>