What does insulation do? How does it make my house warmer?

Insulation doesn’t “heat” an area, it simply slows down heat movement through building materials. Since heat will always move to a colder source, in cold climates, insulation slows the heat from leaving the house and in hot climates insulation slows down the hot outside air from entering the cool inside. The result in both climates is energy saved by keeping the air conditioner or the furnace from operating as often.
There are many types and forms of insulation, and some are better than others at insulating; however, all work by using dead air spaces or cells to slow heat flow. As an example, one of the most common insulating materials, fiberglass, is made from spun glass, and the actual material has very little ability to slow heat transfer. However, spun glass, or glassfiber, is a good insulator because it creates millions of tiny air pockets between the tiny pieces of glass that slow the movement of heat. In cold climate, it keeps the heat in your home from leaking out (making your home feel warmer and causing your heating system to run less).
To compare the insulating quality of insulations, look for the “R-value per inch.” The R-value relates to the resistance the material has to the flow of heat. The higher the R-value per inch, the better the insulating performance.
In order for insulation to be effective:
– The proper insulation must be selected for the appropriate application
– It must stay in place
– It must be installed without gaps, voids, compressions, and low spots
– It must stay dry
For more information about insulation, see the U.S. Department of Energy Insulation Tips