I think it's teflon
I don´t like the teflon,on one side because it is heavier than POM (1,52g/cm³ - 1,39g/cm³)and on the other it isFCKWand FCKW destroyes the atmosphere.
I'm gonna look for some, at some time. Think I might like a lil reduction in weight, but I'm not sure. I'm still happy with the bog standard metal hubs on my circuses, they're doing fine, barring any hard knocks.
man, you have to get the plastic hubs--you'll never go back. even if you just get the "standard" hubs ... you'll notice a drastic improvement, not only in weight, but your string catches less, grinds are smoother, your string doesnt wear out as fast, and it looks cooler