In the 70's people got whacked by rapidly rising energy costs. People responded by making improvements to their homes to reduce heat loss. There are many minor improvements a homeowner can make that can add up to a significant savings. Heat is essentially motion of atoms and molecules. Cold is the absence of heat.
Heat flows from warm things to cooler things.
And the flow of heat is proportional to the difference in temperature between those two things. Some materials are better than others at resisting the transmission of heat. If you can help it, use those materials to surround your home. There are two primary ways that heat escapes buildings. Heat transfer directly through building materials is one way.