Insulating an attic needs to provide good air circulation between the roof and the insulation. It should also include a vapor barrier.

By far, the most common form of insulation used in an attic is fiberglass. It is usually sold in rolls of thickness between 3-1/2 and 6 inches. The width of the roll will vary between 16 and 24 inches.

Batt insulation comes in lengths of 4 or 8 feet. Blanket insulation is available in lengths from 10 to 70 feet.

Foil- or paper-backed fiberglass also serves as a vapor barrier. The paper or foil is the vapor barrier.