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Learn the Truth
About R-value

R-value only measures how well insulation resists heat movement through the insulation material (called conductive heat flow). The advertised R-value of conventional insulation, usually printed on its packaging, is determined by multiplying its thickness (in inches) by its
R-value/per inch.

R-Value per inch (3.6) x 3.5 inches of insulation = R-12.6. (laboratory R-value)

R-value is a popular way of comparing insulation, but it only tells part of the story of how well insulation will work in your home. Here are three reasons why:

1. R-value doesn't measure air leakage control.

R-value only measures energy moving in and out of your home through the insulation material (conduction). But energy (in the form of heat) can move in and out of your home in three ways:

Click here for an illustration showing common air leakage areas in a home.

Building codes in your area usually set a minimal acceptable level of R-value for areas in a home. But if insulation doesn't help stop random air leakage, it's not helping you control the source of up to half of the energy lost by your home (convection).

To make the best insulation investment consider a product offering the best of both worlds: an ideal level of R-value and control of random air leakage.

2. R-value is based on specific laboratory conditions.

In real homes, the R-value advertised can be diminished if insulation gets wet or if it's installed improperly (cut improperly or compressed into wall cavities).

3. Surprise! More or thicker insulation and higher R-values are not always better.

Most (93%) conductive heat flow (heat flow through a solid) is already controlled by R-12 insulation.  That means doubling R-value (from R-12 to R-24 for example) won't double your savings. Learn more.

Did You Know?
The real R-value of insulation when installed can be as little as 50% of the R-value listed on the package.
(Source: California Energy Commission study)

Did You Know?
A California Energy Commission study showed that a 4% void or gap in installed attic insulation reduced the advertised R-value by 50% in the hottest weather.

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