Rockwool Grow Cubes by Grodan - DM 32G 40 /40 HUGO. 6" X 6" X 5.5" Wrapped. Sold individually Extra large cubes for growing full grown plants.Plastic wrapped rockwool cubes guide roots downward. You can set them on top of other rockwool cubes / slabs or use other growing media like Silica Stones for the roots to grow into. Rockwool cubes with holes in the top are designed to have the smaller rockwool cubes fit into them. This would be after you see roots start to emerge from the smaller cube.