a substrate used to grow plants hydroponically; an extruded wool-like product formed through a process of melting rock and extruding it into threads and pressing it into loosely woven sheets at high temperatures
Inert, soilless growing medium consisting of woven, thin strand-like fibers made from molten volcanic rock and limestone, which is heated to over 2900 degrees F, extruded, and formed into slabs, cubes and blocks.