What type of sheath does varnished-cambric insulated cable typically have?

Varnished-cambric insulated cable is characterized by its sheath, which is typically made of lead. This choice is significant because lead sheathing provides excellent protection against moisture and mechanical damage, making it ideal for use in environments where durability is crucial. The lead sheath also helps prevent electromagnetic interference, ensuring that the performance of the cable remains stable and reliable.

When considering the other materials listed, plastic, rubber, and metal are not typical sheathing materials for varnished-cambric insulated cables. While plastic and rubber can offer insulation and some protection, they do not have the same level of moisture resistance and mechanical protection that lead provides. Metal sheaths, although protective, do not align with the traditional composition and historical design of varnished-cambric insulated cables. Thus, lead emerges as the correct answer due to its unique properties that cater to the specific requirements of this type of cable.