Good heat insulators are materials that are poor conductors of heat or thermal energy. Examples are plastics, wood, gases, etc. Heat insulators are materials that do not allow heat energy to be transferred within them.
On the other hand, poor heat insulators are materials that are good conductors of heat energy. In other words, poor heat insulators are thermal conductors. Examples of poor heat insulators are iron, copper, aluminum, brass, steel, silver, etc. To understand this better, you can also refer to good heat insulators as poor heat conductors. Similarly, poor heat insulators are also known as good heat conductors.
Good heat insulators or poor heat conductors are materials that cannot transfer heat. On the other hand, good heat conductors or bad heat insulators are materials that can easily transfer heat. Examples of good heat insulators are gases. This is because gas molecules usually resist heat transfer.