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Fact or Foe: Spray Foam Loses Its R-value Over Time

Does Spray Foam Insulation Lose R-value Over Time?

A common myth surrounding spray foam is that it actually loses some of its R-value over time. Believe it or not, this is NOT a myth! That being said, it is probably not losing R-value in the way you are thinking…

Let’s take a look at how spray foam loses its R-value, and how manufacturers test and rate their foam.

What is R-value?

R-value is simply a material's resistance to thermal change. A great example is a duck! A duck achieves this resistance by trapping tiny air pockets in its down feathers. These millions of trapped air pockets keep its body heat from escaping and allow the duck to swim in cold weather without any fear of freezing.

How Does Spray Foam Develop R-value?

Both open and closed cell insulation works the same way (as in the duck example above)…

Open cell traps ambient air particles in it as it is sprayed, while closed cell actually traps its own gas in it as it is sprayed. This gas is referred to as the “blowing agent” and is what makes the foam expand. This blowing agent is even more efficient than regular air at resisting thermal change.

This is why most closed-cell foams have a higher R-value than open-cell foams.

How Does the R-value of Spray Foam Change?

As foam ages, it will degrade very slightly and lose some of this blowing agent. To most consumers’ surprise, this happens in the first 24 hours. From there, its loss tapers off until it gets to effectively zero after about 6 months.

How Does the Change in R-value Impact Spray Foam Packaging?

Because of this loss of R-value, manufacturers are required to age foam for 6 months to a year and measure its advertised R-value. This is referred to as the “Aged R-value” The foam that we normally use is Johns Manville Corebond IV. This foam has an Aged R-value of 7.2/inch. Its newly installed R-value is probably closer to 7.8/ inch. (Manufacturers typically don't publish these numbers. This is an estimate based on talking to foam manufacturers and training that we have attended).

Do Other Types of Insulation Lose R-Value?

It is worth noting that other insulations will lose R-value over time in different ways. Fiberglass or blown-in insulation’s performance is more susceptible to rodents and moisture. It is also much more likely to settle over time or be affected by future home improvements.

Is Spray Foam Insulation the Best Insulation Option?

When you utilize spray foam, The R-value that is installed is the R-value that you can expect your foam to perform at for the life of your investment, providing years of comfort to you and your family.

Spray foam remains the best, and premium option for insulation.

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