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Blanket insulation—the most common and widely available type of insulation—comes in the form of batts or rolls. It consists of flexible fibers, most commonly fiberglass. You also can find batts and rolls made from mineral (rock and slag) wool, plastic fibers, and natural fibers, such as cotton and sheep's wool.

Batts and rolls are available in widths suited to standard spacing of wall studs, and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without facings. Manufacturers often attach a facing (such as kraft paper, foil-kraft paper, or vinyl) to act as a vapor barrier and/or air barrier. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed. A facing also helps facilitate fastening during installation. However, it's recommended that you use unfaced batts if you're reinsulating over existing insulation.

Standard fiberglass blankets and batts have a thermal resistance or R-values between R-2.9 and R-3.8 per inch of thickness. High-performance (medium-density and high-density) fiberglass blankets and batts have R-values between R-3.7 and R-4.3 per inch of thickness. See the table below for an overview of these characteristics.

Table 1. Fiberglass Batt Insulation Characteristics
Thickness (inches)
R-Value Cost
Cost (cents/sq. ft.)
3 1/2 11 12-16
3 5/8 13 15-20
3 1/2 (high density) 15 34-40
6 to 6 1/4 19 27-34
5 1/4 (high density) 21 33-39
8 to 8 1/2 25 37-45
8 (high density) 30 45-49
9 1/2 (standard) 30 39-43
 12 38 55-6

*This table is for comparison only. Determine actual thickness, R-value, and cost from manufacturer and/or local building supplier.

One unconventional fibrous insulation product combines two types of glass, which are fused together. As the two materials cool during manufacturing, they form random curls of material. This material is less irritating and possibly safer to work with. It also requires no chemical binder to hold the batts together, and the material even comes in a perforated plastic sleeve to assist in handling.

Installation & Cost

The maximum thermal performance or R-value of blanket and batt insulation depends heavily on proper installation.