This white 16 AWG (American Wire Gauge) 4 conductor Speaker cable is CM rated for in-wall use, though it need not be used strictly in-wall. It comes in a 500 foot pull box and is ideal for wiring the speakers in your home theater or house to your receiver. Each conductor (wire) is composed of 65 0.16 mm strands made from pure copper which provides the optimal conductivity/low resistance to drive high quality audio to your speakers. Our speaker wire is made from pure copper. Some companies use the marketing term oxygen free copper which really means there is no iron oxide in the wire. When oxides of iron are in the copper, the conductivity of the wire reduces due to the higher resistance of the iron oxide. So it is in your best interest to install speaker wire made with pure copper like ours are. Another misnomer is that copper clad aluminum is the same quality as pure copper; this is false. The resistance (Ohms) between the two differ and as resistance in the cable increases the power delivered to the speaker is reduced. The sound will be lower and can lose some of its quality. If copper's conductivity, due to resistance, is rated at 100% then aluminum's conductivity would be rated at 61%. In order to deliver the same quality of sound with aluminum one would need a much larger gauge.