We offer rockwool propagation blocks and net containment cups for the rockwool blocks. Rockwool is an ideal substrate for growing almost any plant. It is made from natural volcanic rock which is reheated and formed into “wool-like” fibers. These fibers are sterile and are ideal for proper root growth. Seeds or small rooted plants are placed in the block which goes into the containment cups which are placed into the hydroponic culture trays or tubes. Larger cubes (HP-843) have a 1 1/2″ diameter hole that will accept the smaller cube. Used for larger plants like tomatoes, cucumbers, early stage of trees and bushes etc. Rockwool blocks can only be used once since the roots grow within the substrate.