What make is your water jet, Hopkirk? My teeth are very cramped and it is impossible to use dental floss (even the dentist can't do it) and my jet is fantastic.
No it's not. While it most certainly is made of plastic, the nylon fibers woven into floss are stronger and more resistant to damage than ordinary plastic, so they don't break or fray. To make them even stronger, nylon filaments are coated with wax or another polymer. This coating also ensures that the floss slides smoothly between your teeth as you floss.