Are there also non-conductive foils (so-called insulating foils)?

Yes.

Generally speaking, membrane keyboards are made up of three layers of film, one on top of the other. While the upper and lower layers are made of conductive material, the middle layer is made of non-conductive material. It is therefore nothing more than an insulating film. It has holes in the area of the input elements.

The insulating film thus ensures that there is sufficient distance between the upper and lower films. The contact of a keypad is only closed (and the function triggered) when the upper film touches the lower foil through the hole as a result of the pressure.