Some GreenGuard siding underlayments have a reflective surface and claim a higher R-Value. How does this work?
Reflective surfaces reflect (do not emit) radiant heat. For example, our 3/8″ thick siding underlayment has an R-Value of 1.5. With a reflective surface, the effective R-Value of that product can be as high as 3.6, when installed using a ½” uniform, parallel dead air space on the reflective side. This follows the “ASHRAE Handbook of Fundamentals” basic principles of reflective insulation properties. With the air space partially achieved, the effective R-Value is something between the 1.5 of the foam and the maximum 3.6. Be aware that some manufacturers may make misleading claims of very high R-Values achieved with reflective surfaces. For information on reflective surface thermal performance, click here to visit the Reflective Insulation Manufacturers Association website.
