The findings showed that students understood the meaning of good insulator and conductor materials. However, they still held the conception that a material, which was good for keeping hot objects warm, could not keep cold objects cool as the reported by Lewis and Linn (1994). This view might come out from their experiences of keeping hot water by using thermos which made of metal (outside). Additionally, Libyan students had difficulties in concepts of insulators similar to Western students. Both thought that particular materials were good for keeping hot objects warm and cold objects cool.