Both mineral wool (rock wool, slag wool) and glass wool (fiberglass) are classified in HTS Chapter 70, but they fall under distinct headings based on fiber composition. Rock wool and slag wool are made from basalt or industrial slag, while glass wool is produced from silica-based glass. The distinction matters because duty rates and any applicable antidumping orders may differ between the two fiber types.

Insulation-grade glass fiber (loose wool, batts, rolls) and reinforcement-grade glass fiber (rovings, mats, woven fabrics) are classified under different HTS headings even though both originate from glass fiber production. Reinforcement forms used in composites manufacturing are often classified in Chapter 70 headings specific to woven or non-woven glass fabric, while loose insulation falls under a separate heading — and antidumping orders may cover one form but not the other.