What is this type of membrane keypad called

[Alex Eisenhut]

My Commodore SX-64's keyboard became harder and harder to type on, so I opened it up to clean the contacts.

I am not sure yet where the problem lies, usually it's the carbon "pill" contacts.

But what exactly is this sheet? It's awfully thin yet seems to be a multi-layer sandwich. What is it called? Who makes this kind of stuff?

I contacted Mitsumi and they just told me they have no info on old junk vintage stuff.

[amyk]

Mylar or some other plastic sheet with silver deposition tracks. Membrane keyboard manufacturers will make it.

[Alex Eisenhut]

There's no silver here, and it's too rubbery to be Mylar.

[SeanB]

It is silicone rubber, and you do get repair kits for those keyboards which have that membrane in them as a new part, as the silicone wears out and the carbon printed tracks go high resistance. however try first cleaning with a lint free cloth and gentle rubbing of the gold PCB and the black printed side with isopropyl alcohol, nothing stronger than ethyl alcohol 90% or pure isopropyl alcohol, to remove any deposited film that prevents contact. Light rubbing, as that carbon ink will be very fragile now.

[Alex Eisenhut]

Yeah but I think the trouble is the set of contacts between the PCB and the membrane, it was under pressure with a metal stiffener held in place with two screws. Bad contacts there would impact all the keys, I couldn't really find a bad pill in the matrix, but this set of contacts looks bad.
But I tore it off the PCB so now I'm in trouble.