An example of a bad insulator is glass. An insulator is a material that does not allow much heat or electricity to pass through easily.
Examples of good insulators are polymers and ceramics. But, unlike ceramics, polymers melt at a low temperature. So, they are not suitable materials for anything that would experience a high temperature. In the case of glass, it is not an appropriate material for external doors such as patio doors of homes in very cold temperature zones because of its tendency to lose so much heat.
Glass is widely used in tableware such as bowls and packaging such as food storage jars and bottles for drinks. It is also used in electronics, automobiles, fiber optic cables and others.