There are three types of film base that have been commonly used.

(1) The first is Cellulose Nitrate. This is HIGHLY flammable and has long since been discontinued.

(2) The second is acetate. Acetate deteriorates over time and gives off acetic acid (vinegar). Most still and motion picture camera film is acetate. Film archives all over the world battle to conserve acetate film base.....a significant issue.

(3) The third type of film base is mostly used for 35mm motion picture prints. The film that is projected at most cinemas is polyester or Estar. Acetate is easy to tear whilst polyester/estar is almost impossible. There are problems with polyester as it is so strong that it can damage the projector mechanism if a problem doesn't easily snap. There are also coating and static electricity issues with polyester. The film manufactures have overcome the latter two issues. Polyester is reputed to have far better archival properties than acetate.

Hope this helps.