The treatments applied to "fire retard" have been listed as environmental toxins when in their original form (liquid). I would have to recommend that you not use treated fibers.
If you go to Walmart (i know, evil) you can purchase bulk cloth that you can then cut to fit exactly. This is then machine washable, use baking soda and warm cycle. Also use an extra rinse. Air dry. If you make enough of these you will always have plenty on hand to use.
This will save you money.