noun
: any of various light-weight vitreous materials produced in the form of fibers that resemble wool fibers or glass fibers and that are used as such or after conversion into granular form, felted form (as in batts, blankets, or boards), or molded form chiefly in heat and sound insulation, in insulating cements, and as filter media: as
a. : slag wool
b. : rock wool
c. : glass wool