Fiberglass blanket insulation is the most common type of home insulation in the U.S. It's sold in both rolls and batts (precut strips), so it's easy to buy and handle. Cotton blanket insulation is similar to fiberglass, with about the same R-value per inch of between 3 and 4. (R-value determines insulating power. See our What to Look For page for more information.) Cotton insulation is easier to work with -- it doesn't irritate your skin and mucous membranes like fiberglass does -- but it costs about twice as much.
Blanket insulation is used in walls, attics, floors and ceilings where there are studs or joists. Experts say installing this type of insulation it is a fairly easy DIY project, though care must be taken not to compress it, thus reducing its insulating capacity. It's also important not to leave small gaps between pieces of insulation or between the insulation and obstructions like plumbing stacks, which also can reduce efficiency. Because of these difficulties some experts prefer loose-fill to blanket insulation, though blanket insulation is still used more than any other type.
Both cotton and fiberglass blanket insulation require a vapor barrier to protect against moisture, and rolls or batts can be bought with a facing of Kraft paper, foil or another material that acts as a vapor barrier and an air barrier. If you install the insulation on top of existing insulation, however, you should use unfaced batts or rolls. Both types of blanket insulation are fire-resistant; cotton is treated with nontoxic chemicals to resist both fire and pests.
Need help figuring out how much insulation and what R-value you'll need? See our What to Look For page for details on those calculations, plus installation considerations and other factors to consider.