What other materials, apart from flesh, can you use to interact with an iPhone Touchscreen? The other day I was in my car and though I'm a little unsure about what candy bar wrapper I used but I believe I moved my screen using a candy bar wrapper.  I keep thinking it was a York Peppermint Patty wrapper, but I could be wrong about that, either that or a Laura Bar wrapper.

I'm told an iPhone has a Capacitance Touch Screen which is different from earlier models of touch screen which relied on clicking or something else, but it's clearly not the same thing.

Using the old screens you could use a paper clip or whatever to interact with the phone, but with an iPhone it's the tip of your finger, and apparently a few other materials. 

In particular I'm interested in being able to tap with it.
I have several pens with a "rubber" type end that work the screens fine.

Must be a material that is treated...