At Hyrel, we readily disclose that you can use any 1.75mm filament you want, provided it prints at 250C or less. Or 350C or less with a different head.

Or any wax, clay, paste or emulsifiable that prints at room temperature, or up to 100 or 150C, with different heads.

Or any photoinitiated polymer that crosslinks at a wavelength of between 365 and 450nm, at room temperature or heated up to 100C, with different heads.

In fact, we don't sell filament or other print media. Just the printers.