Grodan A-OK 25/40 1 Inch Starter Plugs, Individual sheet of 200 Comes labeled with instructions in a shrink-wrapped sheet that fits a standard tray Tremendous capacity for absorbing nutrient solution while retaining plenty of oxygen for rapid plant growth Designed for seed and cutting propagation prior to "blocking on" into larger growing blocks Grodan Stone wool (Rockwool) is made from molten rock spun into cotton candy-like fibers