What Is the R-Value for 4 Inch Batt Insulation?

Faced and Unfaced

• Fiberglass batts come in two styles, faced and unfaced. Faced has a moisture barrier on one side, which typically has flaps on both sides of the batt for easy installation. A batt is placed into a wall cavity, and the flaps are stapled to the studs on both sides. Wall batts are nominally 16 inches wide and nominally 4 inches thick to fit the wall cavity; the actual thickness conforms to the 3 1/2-inch thickness and 15-inch inside dimension of stud framing.

Heat Resistance

• Insulation effectiveness is measured in R-value, its capacity to resist heat. Standard fiberglass has an R value of 3.0 to 3.2 per inch. That would give a nominal 4-inch wall batt an overall R value between 10 and 12. Actual R values, however, will vary by manufacturer. It will even vary within manufacturers by type of product. One manufacturer's product line has batts with R values varying from 11 to 15.

High Density

• High density (HD) fiberglass batts have a higher R value, from 3.6 to 4 per inch. A typical high-density fiberglass batt will have an R-value of 15 for a 3 1/2 inch thickness. The actual R-value of high-density batts will vary to as little as about 12.6, again depending on the manufacturer and the specific brand. Many manufacturers produce more than one type of batt.

Facing

• Facing can affect R-value. Facing is typically kraft paper, and batts are labeled on the face by R-value. Unfaced insulation has no outer covering to block heat or moisture; manufacturers typically provide a code to indicate the R value, but these codes vary by maker. Some faced batts are covered with a foil barrier, which not only blocks moisture but also adds to the heat resistance.