A protective helmet worn for riding, typically consisting of a shell of impact resistant plastic or resin and a layer of polystyrene which acts as a shock absorber. The helmet may be covered in material such as velvet and is usually padded and lined with an absorbant fabric. The hat is fixed to the head with a harness that is attached at three or more points. Riding helmets are designed to protect the rider's head in case of a fall or from the impact of a horse's hoof. They cover more of the head than helmets in other sports. Designs of helmet vary, particularly with regard to the outer surface, the thickness of the shock absorbant layer and the amount of ventilation. In most countries, riding helmets are subjected to safety tests which give them a national or internationally recognised standard of safety. There are different regulations regarding their use in equestrian sporting disciplines; most disciplines require riding helmets certified to certain standards to be worn in competition.