Rockwool

trademark

Rock·​wool ˈräk-ˌwu̇l 

—used for mineral wool made by blowing a jet of steam through molten rock (such as limestone or siliceous rock) or through slag and used chiefly for heat and sound insulation

Kids Definition

rock wool

noun

: a material resembling wool made by blowing a jet of steam through melted rock and used chiefly for heat and sound insulation