The construction details of the TPI modular test leads help set them apart from the competition. Silicone insulation wraps the lead wire. They are double insulated for safety. Double insulated means two layers of silicon insulation. A white base is applied followed by a colored top coat. A white strip appears on the wire when the colored coating is worn, nicked or cut alerting the user that it is time to replace the test lead. The silicone coatings are flame retardant, very durable and more flexible than inexpensive PVC coatings. The silicone insulated leads also meet stringent agency approvals such as cULus and IEC ratings.