Final answer:
A good insulator slows the passage of heat rather than preventing it completely, helping to regulate temperatures by reducing heat flow.
Step-by-step explanation:
An insulator is a material that is poor at conducting heat, which means it effectively slows the passage of heat rather than preventing it entirely. Good insulators, such as fiberglass and air trapped in small spaces, use this property to reduce the rate at which heat flows into or out of a space. In the context of a house, insulation is used within walls and attics to limit the conduction of heat from inside to outside during winter months, and vice versa during summer months, which helps maintain a comfortable temperature inside regardless of the temperature variations outside.