I wouldn't use it.....filter media is not expensive if you use stuff from the pond dept of your LFS, just needs cutting up with scissors or electric carving knife.
Here's an even better idea: rather than risking fire retardants in pillows, go to a craft store or a 2 dollar store (you know the 'cheap chinese junk' shops) and buy teddy bear/cushion stuffing. It's far, far cheaper than purpose made filter media and I have never had a problem with it as long as I rinse it first.
thats where i bought it last time..the price have came down quite alot..thanks next time in it cupar ill get some filter floss..i dont need it right away but will in the near future..