Grodan, 30 Pack, 98 Count, A-OK Plug, Made From Molten Rock Spun Into Cotton Candy Like Fibers & Then Compressed Into Cubes, Blocks, Or Slabs, Unique By Making Different Types Of Fibers, Supports The Requirement Of The Plant In The Different Plant Stages, Absorbs Nutrient Solution While Retaining Plenty Of Oxygen For Rapid Plant Growth, Seedlings Started In Cubes Are Easily Transferred To Blocks & Then Onto Slabs, If Desired, Can Be Transplanted Into More Traditional Planters & Growing Mediums.