Expanded-clay aggregate, or "exclay", is a lightweight ceramic aggregate ("LWA"), used in construction and hydroponics.
Exclay is produced by processing natural clay which is finished to the shape of round pellets. The clay is expanded by thermal treatment in a rotating kiln operating at temperatures about 1100°C. Exclay lightweight aggregates are available in various densities and grades between 3-32 mm (0.8-8.1 inches). It packaged in sacks of 25-50 liters. The density of exclay pellets is approximately 350 kg/m³.
Exclay is an environmentally friendly product composed of mostly of naturally occurring clay and has a long life span.
To make the exclay, toxic residues such as used oil and many kinds of petroleum gas oils are used as fuel for production. Such fuels may leave toxic residues in the final product.
- Hammer Tor Arne: "Materials for Buildings and Structures" Co-Authors: Klaas van Breugel, Steinar Helland, Ivar Holand, Magne Maage, Jan P. G. Mijnsbergen, Edda Lilja Sveinsdóttir  (PDF)