Expanded clay is a lightweight, porous material made by heating clay to high temperatures. This process causes the clay to expand and form small, round pellets. These pellets are often used in construction, gardening, and hydroponics due to their excellent drainage and aeration properties. In gardening, expanded clay is popular as a growing medium because it helps retain moisture while allowing excess water to drain away. It is also used in green roofs and as a component in concrete to improve insulation and reduce weight. Its versatility makes it a valuable resource in various applications.