Lightweight expanded clay aggregate (Leca) granules are light, porous, and have good resistance to crushing. Used in, among others, hydroponics, aquaponics, orchids, and ordinary soil gardening.
This aggregate is made by heating clay to 1200°C in a rotary kiln. The yielding gases expand the clay, causing small bubbles to form a honeycomb structure. These spaces allow nutrients to be taken up and gradually released to the plant. They also allow oxygen to reach the roots of the plants.