Thats what I said so I googled it...
Seramis clay granules are designed to provide horticulturalists with a clean, safe and versatile planting medium. Special water retention features allow each granule to store more than 100% of its weight in water at the same time as draining any excess. Because Seramis has a stable structure and will not decompose or compact, the water storing capacity is permanently maintained. The space between the granules also remains stable and allows air to permeate through the roots. These characteristics give growers the opportunity to control watering regimes, nutrient formula, air flow and PH levels. This flexibility benefits plants and gardeners from any horticultural background.