People who use fleece/material in their rat cages?

Dont your rats shred it to pieces? How often do you have to replace it (not replace to wash, I mean replace it when it gets torn to shreds lol! I was thinking about this as a cheaper alternative to cardboard shreds for my rattyroos, but my rats are really bad material shredders so it might not be cheaper lol! I like the idea of just shaking the poo off and bunging it in the machine though!