Function

• Insulation levels are indicated by an "R" value. The U.S. government's Energy Star website focuses on energy efficiency, and it notes that the recommended "R" value for attics is at least R-38. That requires installing insulation that's 10 to 14 inches thick. The "R" value is a measure of how well insulation resists the flow of heat into and out of the attic. Insulation helps control that flow to reduce the costs of heating and cooling a home.
  
  

Features

• Fiberglass batts are often added in attics because they can easily be placed on top of insulation that may already have been installed. The batts look like thick blankets, and they can be cut to fit between the joists or beams that typically support the walls and floor of an attic. The batts are made of thin fibers of glass that trap air to control heat flow.
  
  

Considerations

• The U.S. Green Building Council's website lists cellulose among environmentally friendly types of insulation that can be used in attics. Cellulose is made of recycled newspaper, and the council asserts it requires up to 30 times less energy to manufacture than fiberglass. A blower is used to force small pieces of cellulose into wall and floor cavities between joists. However, the council notes that cellulose can eventually settle or flatten in some cases, which could hamper its insulating properties.