Cob, cobb or clom (in Wales) is a natural building material made from subsoil, water, fibrous organic material (typically straw), and sometimes lime. The contents of subsoil naturally vary, and if it does not contain the right mixture it can be modified with sand or clay. Cob is fireproof, resistant to seismic activity, and uses low-cost materials, although it is very labour intensive. It can be used to create artistic and sculptural forms, and its use has been revived in recent years by the natural building and sustainability movements.