For roll films polyester can be distinguished from acetate with a simple test. Simply raise the film reel up to a strong light source and view the film ‘edge on’, through the spokes of the reel. Alternatively, place the reel of film on a light box. Polyester film will transmit much more light through the edges than acetate or nitrate. Nitrate will typically appear opaque in this test, and while some light may ‘pipe’ through acetate film viewed edge on, much more light will pass through polyester film.