Fiberglass is a man-made heat resistant material that is used in many industries for electrical and thermal insulation.
Wool is the best natural fiber used in heath rug manufacturing. Wool is highly durable and will not melt, and wool hearth rugs will extinguish themselves naturally should they catch fire. Unlike fiberglass, wool hearth rugs can be singed by flying embers or sparks, but these black marks are usually easy to brush out.
Wool rugs are among the most beautiful of all fireplace rugs, but are more expensive than nylon or polyester rugs.
The bad news about nylon hearth rugs is that contact by a burning ember may cause a small, black melted spot that can't be removed. The good news is that these marks won't be on your carpet or wood flooring. Nylon also has a higher melting point than other synthetic fibers used to make fireplace rugs.
Nylon hearth rugs are the best choice if you want simple and inexpensive protection for your floor.
Synthetics: Olefin, Polyester, Polypropylene
Hearth rugs made from synthetic materials other than nylon will show more burn marks, but they're also very functional and cost-effective. If you purchase a hearth rug made from a synthetic material such as olefin, polyester, or polypropylene, be aware that some rugs feature a decorative fringe that may be flammable.