Rockwool
Rockwool has long been a popular media for growing hydroponic fruits, vegetables and herbs.
Rockwool doesn’t score well on the environmental scale. It’s not a natural material. Manufacturers use combine chalk and rock and then heat them up to around 3,000 degrees Fahrenheit. Next a stream of air is blown through it, resulting in extremely thin fibers of the rocky material. As the strings are blown out, they bunch together and form the material that you see for sale at the local hydroponics store.
Rockwool is an insulation created by spinning together natural and artificial metal oxides and minerals. It is commonly used across the home building industry as an asbestos alternative though data suggests that the compound may be just as harmful.