What Is a Good Insulator?

Basics

• Heat naturally flows to cooler areas. In the summer, outdoor air causes your home to get warm. In the winter, your heated air escapes to the cooler air outside, making your house colder. Insulation slows down the transfer of heat by resisting the flow of heat. The same principle helps you slow the loss of body heat when you wear a jacket or use a blanket. In fact, some types of insulation are essentially blankets for your home.

Types

• Many types of insulation exist, including blankets made from fiberglass, wool, cotton or other fibers. Polystyrene and other types of foam, which you can install as part of concrete or as foam boards, will also slow heat transfer. Loose-fill insulation, which is made from fiberglass, cellulose and other materials, is blown into wall cavities and hard-to-reach places, while other types of foam is sprayed in to irregularly shaped areas.

Efficacy

• The efficacy of an insulator is measured by its R-value, or thermal resistance value. R-values are usually indicated per inch of material. Higher R-values mean a material insulates more effectively. For example, cellulose loose-fill insulation has an R-value of approximately 3.7 per inch, while expanded polystyrene has an R-value between 3.5 to 4.5 per inch. R-values vary by manufacturer and installation. Installing two foam boards, for example, doubles the R-value, while installing loose-fill insulation at a density lower than the manufacturer's recommendations decreases the R-value.

Choosing Insulation

• The best type of insulation for your home depends on several factors, such as your budget, space constraints and local temperatures. For example, blankets are easy to install in unobstructed space, but loose-fill or spray foam is better for cavities or irregularly shaped areas. Whether you are adding insulation as you build your home or retrofitting an established home also affects your choice; some types of insulation can only be built into your home during construction or added during extensive renovations.