Grodan Rockwool Cubes 3 x 3 x 2.5 are cubes  of stonewool (rockwool) that have a grooved base. Promoting drainage to avoid root rot. Grodan Rockwool is pH neutral. Making it easy for you to maintain the ideal hydroponics  pH value of 5.5 – 6.5. Each gro-block is wrapped in white plastic, For shape stability.  Rockwool Cubes have evenly distributed air pores that encourage your plants root growth throughout the entire block.