A cel, short for celluloid, is a transparent sheet on which objects are drawn or painted for traditional, hand-drawn animation. Actual celluloid (consisting of cellulose nitrate and camphor) was used during the first half of the 20th century, but since it was flammable and dimensionally unstable it was largely replaced by cellulose acetate. With the advent of computer assisted animation production, the use of cels has been practically abandoned in major productions.