 What is an external CAT 6 cable? External CAT 6 cable is a cable designed for outdoor installation. Instead of a PVC also sheathing it has a polyethylene P.E. sheath. Unlike internal cables which are generally grey, violet, orange and blue this cable is standard in black. The P.E. sheath provides environmental protection from external factors such as moisture and temperature. However, for additional protection, a steel wired armoured cable is used. P.E. external sheathing doesn't offer additional structural protection. It has the same structural protection as that of an indoor cable.