Does foam board lose R-value over time?

Author: Willis Blick  |  Last update: Friday, November 14, 2025

Extruded Polystyrene (XPS) A popular rigid insulation choice, XPS features an initial R-value of R-5 per inch. That said, the long term R-values of this foam board decline over time.

Does foam board insulation lose its R-value?

An initially rated R-value 5.0 XPS product will eventually drop to closer to an R-value of 4.3. Since EPS is made up of only air and polystyrene, its R-value does not depreciate over time.

Does foam insulation deteriorate over time?

The chemical composition of spray foam creates a stable, unreactive material that resists degradation over time. Unlike other insulation materials that can rot, decay, or be affected by pests, spray foam insulation remains unchanged and effective for decades.

Does foam board insulation shrink over time?

Regarding dimensional stability, Dow Styrofoam XPS, states that the maximum shrinkage that can be expected is 2%. Over a 96" long board that's 1.9 inches.

How long does foam board insulation last?

Foam board insulation, including types such as polystyrene, polyisocyanurate, and polyurethane, has a lifespan of 30 to 50 years. This type of insulation stands out for its moisture resistance and high thermal resistance, which contribute to its longevity and effectiveness in various applications.

Busting R-value insulation MYTHS

What are the negatives of foam board?

Cons of a Foamboard

Foamboards can get discolored, disintegrated or warped if left under the sun or rain. It can be used for a short outdoor event and not as a permanent outdoor display. Also keep it away from your bathroom or kitchen as steam can create moisture, affecting the foamboard.

When should I stop wearing foam boards?

FOAM/BOARDS: Add foam inside your compression garment within 24 hours of surgery (see video above) for any liposuction areas to create even compression. Recommend wearing a polyester layer directly over the skin first to prevent skin irritation. Foam is continued for 1 month post op minimum.

Does foam insulation go bad?

Spray foam: 80-100 years with correct installation

Even if your insulation is still “technically good” according to manufacturer's recommendations, you still need a professional to take a look if you have concerns. The energy-efficiency experts agree: Insulation can lose its effectiveness over time.

How long does it take foam to deteriorate?

Estimates vary from a few years to a million years. As always, there are various environmental conditions to consider with each scenario. It's a daunting topic to unpack, but it's absolutely crucial we do. In this article, we'll unpack why plastic foam is bad and whether it truly decomposes or not.

Can I put foam board over insulation?

Yes, foam board insulation is an excellent complement to batt insulation. Foam board insulation can add insulation and eliminate thermal bridging when used in wall and ceiling assemblies insulated with batts. It can potentially replace the vapor barrier and house wrap as well.

What is the downside to foam insulation?

Spray foam insulation is a good insulator in terms of keeping a room warm or cool. But its many downsides outweigh the benefits. These include, making it more difficult getting a mortgage, potential health issues, environmental damage, ventilation issues and a lower home valuation.

Does insulation lose R-value over time?

Therefore, insulation whose thickness changes for any reason over the years of use will see a decrease in its R-value, thus reducing its insulation effectiveness, and in exceptional cases, dropping to zero.

Does foam disintegrate over time?

Because it takes hundreds of years to decompose, if it decomposes at all, polystyrene foam is effectively not biodegradable. Research suggests that plastic foam lasts in our environment for thousands of years and therefore threatens the health of wildlife for a long time.

Does doubling foam board double the R-value?

For example, our polyiso rigid foam boards have R-values between 6.5 and 6.8 per inch. If two layers are installed, it doubles the R-value and cuts heat/conditioned air loss in half. For reference, plywood has an R-value of 1.25.

What is the life expectancy of foam insulation?

Spray foam insulation lasts for 80 years to 100 years, but closed-cell spray foam will last a little longer than open-cell spray foam. For many homeowners, this lifespan will extend beyond the entire time they own their house. Closed-cell spray foam lasts longer than open-cell spray foam due to its rigid structure.

Is there a big difference between R13 and R15?

R15 insulation offers slightly better thermal insulative properties than R13. Some of its formats are a fraction of an inch thicker than R13, making it more effective at helping with energy efficiency. However, the difference is minimal.

Does foam insulation shrink over time?

With spray polyurethane foam, there can be shrinkage; however, there does not have to be. The shrinkage can be severe to the point of twisting wood framing members or denting metal. Normally, the foam will give way within itself and crack open – this is referred to as thermal cracking.

What is the shelf life of foam?

Depending on what type of foam concentrate you have, the typical shelf life will vary. Protein type concentrates have a shelf life of about 7 to 10 years. The synthetic type concentrates, which are the AFFF, ARC type AFFF, Class “A” and High-Expansion concentrates, have a shelf lives of 20 to 25 years.

What are the problems with foam board insulation?

Foam Board Insulation Problems
  • Decrease in insulating abilities. Overtime polyisocyanurate foam boards can decrease insulating capabilities. ...
  • Moisture collection. Expanded polystyrene foam boards are made with air bubbles that stop heat transfer. ...
  • Air leakage. ...
  • Improper installation.

How to tell if old insulation is still good?

As a general rule, however, home insulation should be inspected once a year to check for signs of damage, mold, and more. If you see signs of degradation and/or you are experiencing issues such as uneven heating, cold spots, etc., it may be time to upgrade or replace the insulation.

How long does foam board last?

The lifespan of PVC foam board can vary depending on the quality of the material and the environment it is exposed to. High-quality PVC foam board that is properly installed or maintained can last up to 20 years or more in construction applications and up to 5 years or more in outdoor signage applications.

What are the cons of foam boards?

Disadvantages of polystyrene foam insulation board
  • EPS insulation board needs to be hung, and the construction is complicated and the cycle is long;
  • Flammable & toxic. ...
  • Poor material strength. ...
  • Limited strength and load-bearing capacity.
  • Unstable quality.

What happens to foam board if it gets wet?

Can foam insulation get wet? Yes, it can get wet without absorbing water. However, water pressure can damage the foam, potentially compromising its insulating properties.

Can you walk on foam board insulation?

Compressive Strength: Other types of insulation like cellulose or fiberglass blanket carry virtually no compressive resistance, while polyiso rigid insulation boards typically boast a compressive strength of 20 psi or higher. This means you can walk on rigid insulation without damaging it.

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