Over-molds can be made from a number of materials, but PVC is the most common. Pure PVC is very hard and generally unsuited for this application. PVC used in cables have plasticizers added, which make the PVC softer and more flexible. This chart shows how adding more plasticizers lowers the shore durometer number. In the shore durometer scale lower numbers mean softer material. Softer materials are more enjoyable to handle and more flexible, but less resistant to cuts and abrasion.