Originally Posted by Jope
Not leaf, conductive rubber. :-) Leaf switches have two slips of metal that touch when you press the button..
I've "repaired" lots of joysticks, these are an extension to leaf. Inside the rubbery bit is a conductive surface (carbon) which deforms to complete the circuit under pressure and goes back to it's old state when not under pressure breaking the circuit.
It's the same technology as in most modern remote controls.