A product that can be used as a substitute for perlite or sponge rock. Growstone has 40% more porosity than perlite, and is made from recycled glass which is 100% silica. It is a great product to mix with high moisture retentive materials such as coir and peat moss. The GS-2 Soil Aerator size, which is the most commonly used size in orchid potting applications, has granules that are 1/4" to 1/2" in size. The GS-1 Hydrostones (hydroponic/chunky) are 1/2" to 3/4" in size. The smaller bag size is 4 lbs and roughly 9 liters (8.2 quarts) of material.