Cellulose acetate (CA) is used as the base for modern cinema film and for archival copying of deteriorating cellulose nitrate film. It has also been widely used for laminating fragile paper. Unfortunately it has proved to be unstable, breaking down to release acetic acid and the plasticiser. The main cause of film deterioration has been identified: moisture absorption together with the accumulation of acetic acid in the storage cans. The iron of the cans acts as a catalyst. Tests are underway to identify and introduce possible stabilisers into the polymer. The stability differences between cellulose di-acetates and tri-acetates, and the stability of the cellulose nitrate are considered. Tables, graphs and 12 references.