actually, while I know it's often called teflon, is it really teflon that is commonly used?
All the dielectric plate that I've used for circular C-band looked very much like printed circuit board stuff (fiberglass-reinforced epoxy resin), just a lot thicker than a PCB. And recently I had to file the edges of a plate I got with my Titanium LNBF to fit it in an old Polarotor, and filing it produced the exact same smell as you get when drilling/cutting a PCB board.
Also, I think I have seen a Dish Network LNBF that used a transparent dielectric plate - so maybe it was polycarbonate.