Follow the basic rules of common sense:
- Don't make life complicated.
- Don't get pellets.
- Buy fiber-fill.
- Make sure they are fire retardant. If it says on the bag that it meets your State's fire regulation, that is normally good.
- Don't overfill the speakers/sub.
- You can buy them at Wal-Mart or Michaels for less than $3-$4.