These RCA audio cables are made with a solid copper core which is superior to stranded core for sound quality as well as its longevity. Solid copper is a great conductor of electricity and a perfect choice for sending signal between devices. The CL2 rating indicates that the jacket of the cable has been treated with a flame retardant in order to comply with fire safety regulations for in-wall installations. This cable is safe for use through or within walls of residential buildings.