Distortion caused by dimensional differences between the emulsion layer and the support layer, width-wise. Curl in a film is as a result of the film being wound onto an extremely small core, or sometimes no core at all, and then having been left that way for quite some time. The film retains a memory of its position and when unwound attempts to return to the very tight curl it has been in, sometimes for many years. The film needs to be handled carefully, despite the difficulty, as the emulsion or base may crack if the film is brittle. Once stored on a larger core the film will begin to memorise its new form.