The purpose of good wire insulation is to protect the cable from voltage leaks. The single most important factor for rating insulation performance is the material, not the thickness. Silicone, while resisting temperatures of up to 600 degrees will give you the greatest protection. The PROMINI wire sets are 2 layers of high quality silicone. Unlike some other manufacturers which only use 1 layer of silicone over a less expensive inferior layer. Our proudct uses 7mm double wrapped silicone over 19 strand copper core wire. This is the correct wire diameter which fits correctly into the factory type plug and cap connectors.