Cultiwool 6" x 6" x 6" Block with Optidrain (48 Block/Case): Cultilene is a rockwool growing medium designed for seedlings and clones of spun basalt rock fibers. https://www.hydroponicstown.com/cul666-cultiwool-6-x-6-x-6-block-w-optidrain-48-block-case-cultilene