One of the most commonly asked questions we get is “What’s the difference between R-Value and K-Value?". R-Value is commonly used to measure the insulating performance of building materials such as fiberglass insulation that you can buy at Home Depot, Lowe’s or any other lumber yard. R-Values express an insulation's thermal resistance, or the ability to stop heat flow. Although it is not a very common term in the mechanical insulation industry, it’s still a good concept to understand. The thicker the insulation is, the greater the R-Value.
K-Value on the other hand is the measure of heat conductivity of insulation. More specifically, it measures the amount of heat (in BTUs per hour) that will be transmitted through one square foot of 1" thick insulation in order to cause the temperature to rise or fall one degree Fahrenheit from one side of the insulation to the other. The lower the K-Value the better the insulating performance of the material.
The two are somewhat related, as they are both methods of measuring the insulating performance of an insulation product. Differences can also be seen in the scale in which they are measured. For example, the higher the R-Value the greater the insulating performance of the material, whereas the opposite is true for K-Value.
If the K-Value of an insulation is known, then the R-Value can be determined, and vice-versa. To calculate the R-Value of insulation, simply divide the thickness (in inches) by the K-Value. To calculate the K-Value of insulation, simply divide the thickness (in inches) by the R-Value.
Understanding these concepts will help you to know what questions to ask your insulation contractor on your next project. Additional information on the subject can be found on the NIA website.
