Since 1975 the FIA has required that driver clothing be flame retardant so as to offer protection in the event of a fire. That used to mean heavy, five layer, NASA-spec race suits. Nowadays the key is Nomex^®, a fire-resistant, lightweight artificial fibre which undergoes thermal testing in the laboratory. It is subjected to an open flame with a temperature of 300 to 400 degrees Celsius that acts on the material from a distance of three centimetres - only if it fails to ignite within 10 seconds can it be used in a driver’s overalls.