What Are Insulation R-Values?

Insulation's primary function is to reduce heat transfer, and its effectiveness at doing so is referred to as its R-value. An R-value is a measurement of insulation's thermal resistance, or its ability to resist the flow of heat. R-values for home insulation, such as in an attic or wall, range from R-1 to R-60. The higher the R-value, the more effective the insulation is at resisting heat flow.

Factors that Determine R-Value

The R-value of fiberglass insulation is based partly on its thickness.

All insulating materials, and all building materials for that matter, have a corresponding R-value that is based on the material, its thickness and its density.  Four-inch-thick cellulose will have a different R-value than 4 inches of fiberglass. There are also high-density options for most types of insulation, each with a slightly higher R-value per inch than a low-density option of the same thickness. 

Common Insulation Types and Their R-Values

Fiberglass is by far the most popular type of insulation used in the United States.  It comes in two forms: batts and loose fill (blown). [Batt insulation](https://homesteadycom/info-12003942-batt-insulationhtml) typically has an R-value of between 29 and 38 per inch of thickness,.  Higher-density fiberglass can have an R-value of between 37 and 43 per inch. Loose-fill fiberglass is typically rated between 22 and 27 per inch.  Cellulose insulation, which is made from recycled newsprint, is another popular type of loose-fill insulation. Its R-value ranges from 36 to 38 per inch. 

Rated R-Value vs. Effective R-Value

All insulation materials have an R-value assigned by their manufacturer, much like miles per gallon for an automobile.  That value is contingent on a proper installation. Small gaps in insulation, much like a hole in the bottom of a boat, will severely degrade performance.  For example, a 4 percent void in fiberglass batts (gaps between batts or batts not adjacent to joists) can degrade the overall R-value by up to 50 percent. Loose-fill insulation tends to settle over time, which also can reduce its R-value. 

R-Value and U-Value

Even windows, bricks and drywall have R-values.  But with windows, for example, manufacturers advertise their U-value, sometimes referred to as the U-factor. The U-value is the inverse of the R-value.  So in the case of windows, the lower the U-value, the better it performs as an insulator.

About the Author

Adam Flowers has written for Demand Studios since October 2009. He holds a bachelor's degree in journalism from Middle Tennessee State University. His work has appeared in "Relevant" magazine and "Electrical Wholesaling" magazine.

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