Switch film

Switch film is a thin sheet, usually plastic or a similar polymer, cut to fit between the top and bottom housing of a switch before it is reassembled. Because switch housings from the factory often have small manufacturing tolerances, the two halves can wobble slightly against each other, which shows up as extra rattle in the final sound.

Adding film tightens that gap, reducing housing wobble and often making the switch sound and feel more solid, particularly on switches known for looser tolerances. The effect varies by switch model, since some switches already fit tightly and gain little from filming, while others improve noticeably.

Filming switches by hand is fiddly, since the film has to sit flush without bunching, and doing dozens of switches for a full board is time-consuming, which is why some enthusiasts buy pre-filmed switches or switch film sized specifically for a given switch housing. Combining films with lubing usually gives a more noticeable improvement than either mod alone.