GS-1 Hydro Stones, 1.5 CUFT Highly Porous Aggregate, Made From 100% Recycled Glass, Used For Both Traditional & Hydroponic Growing, Lightweight, Clean & Provides More Water Holding Capacity & Aeration To Roots, Use As A Drainage Layer At The Bottom Of Containers, Blend With Coco, Peat, Compost Or Soil To Provide Increased Drainage & Aeration, Or Use Right Out Of The Bag For Hydroponic Growing.