Here's why:

* Electrical conductivity: Sulfur is a non-metal, and non-metals generally have poor electrical conductivity. This is because their electrons are tightly bound to their atoms and don't move freely.

* Thermal conductivity: Similar to electrical conductivity, sulfur's electrons are tightly bound, making it difficult for heat energy to transfer through the material.

Therefore, sulfur is a good insulator for both electricity and heat.