Editing Foam and foil (section)

==Design==
Capacitive switches require three capacitor plates. Two are placed side by side on the PCB. The third is a movable part, whose proximity to the PCB alters the capacitance of the switch and permits detection of keypresses. In foam and foil switches, this third plate takes the form of a disc of metal foil attached to the slider. To allow for [[travel#Overtravel|overtravel]], a thick foam pad is placed between the slider and the foil disc, giving the switch its moniker.

Foam and foil switches were referred to by both [[Key Tronic]] and [[Cherry]] as "solid state". This is an inaccurate approach used to describe the fact that such switches do not use metal switch contacts, relying instead on electronic sensing; they do of course have moving parts.

Foam and foil switches have no capacity for an internal [[return spring]], so this must be fitted to the outside of the switch. A [[buckling rubber sleeve]] can be used instead, to provide a tactile response.