There are several ways to tell if socks are made of cotton: - check the label: the composition of the socks is usually indicated. - feel the socks. Cotton is a soft, supple material. - look at the socks. Cotton has a natural, slightly matte appearance. - test the socks. Cotton is a breathable material. - as a last resort, burn a sock yarn. Cotton burns, leaving a white ash and a smell of burnt paper.