Classical guitar strings are strings manufactured for use on classical guitars. While steel-string acoustic guitar strings and electric guitar strings are made of metal, modern classical guitar strings are made of nylon and nylon wound with wire, which produces a different sound to the metal strings. Classical guitar strings were originally made with animal intestine and silk wound with animal intestine up until World War II, when war restrictions led Albert Augustine Ltd. to develop nylon strings. Nylon guitar strings were put into production in 1948. Strings made from fluorocarbon polymers have since been developed and are the main alternative to nylon strings.