Can I use foam board instead of fiberglass insulation?

Author: Dr. Maya Ondricka Jr.  |  Last update: Monday, April 13, 2026

However, you can use rigid foam board instead of spray or fiberglass insulation where it makes sense, such as in wall cavities that may risk becoming wet or moist.

Can I use foam board instead of insulation?

Yes - interior foam board is a well-tested method for improving thermal performance and comfort in a renovation.

Is foam board insulation as good as fiberglass insulation?

It excels at effectively insulating your home, providing superior energy efficiency. Unlike fiberglass, foam insulation doesn't degrade over time, ensuring it remains effective for the lifetime of your building. This longevity can offset its initial cost, making it a cost-effective choice in the long run.

What are the disadvantages of foam board insulation?

Insulation Foam Boards Don't Work On Uneven Walls

This allows moisture to seep in. Excess moisture can cause mold, mildew, odors, decay, fungus growth and wood rot.

Can foam poster board be used as insulation?

Foam board is commonly used for photo mounting, signage, presentations, architectural models, and insulation.

Foam Insulation vs Fiberglass: The Ultimate Home Insulation Comparison Think Coffee Cups

Does foam board insulation act as a vapor barrier?

Polyisocyanurate (PIR) foam board insulation has a relatively low permeability, meaning it can resist the passage of moisture to a certain extent. However, it is not typically recommended to rely on PIR foam board insulation as a standalone vapour barrier.

How well does foam board insulate?

With R-values ranging from 3.6 to 8.0, rigid foam sheathing has much better insulation per inch than other materials (i.e. plywood has an R-value of 1.25 and fiberglass batts have an R-value of 3.14).

What is the life expectancy of foam board insulation?

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.

Can mold grow on foam board insulation?

Under certain environmental conditions, such as high humidity and the presence of organic pollutants, the surface of polystyrene foam may gradually accumulate moisture and nutrients, thereby providing certain conditions for the attachment of mold.

Do I need house wrap if I use foam board?

House wrap helps prevent moisture damage, but when coupled with foam siding they create an unstoppable force. Moisture Management System for your home: It's estimated that each person uses 80-100 gallons of water per day at home. Instead of that moisture becoming trapped inside the home, foam can help it escape.

Can I put foam board over batt insulation?

Halo Interra foam board insulation can be applied to the studs, covering the batt insulation. To insulate the underside of ceilings. Halo Interra foam board insulation is applied to the underside of the ceiling joists.

Why not to use fiberglass insulation?

Fiberglass insulation is less dense than other types of insulation and does not create an airtight seal, which means air can travel freely through the insulation. This is called air leakage and it's one of the most common sources of energy loss in a house.

How thick should foam board insulation be?

How Thick Is Rigid Foam Insulation Board? Rigid board insulation generally comes in standard thicknesses ranging from ½ inch to 2 inches. It is possible for homes located in extreme climates to order specialty thicknesses of up to 6 inches directly from certain manufacturers.

Is foam board better than fiberglass insulation?

Basements: Indoors, rigid foam board is better than fiberglass insulation for basements. It's the material of choice on walls where the insulation will touch masonry.

Do you need a air gap with foam board insulation?

Insulation boards are no exception to this rule, and it's important to leave an air gap between them and the surface they're installed on.

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.

Does foam board insulation need to be covered?

That said, it's still advisable to cover any foam board insulation exposed to the Sun within 30-60 days at the most.

Can too much insulation cause mold in walls?

Many of us know what causes mould; when moisture is trapped in the rooms of you home. Sometimes, there is insufficient insulation in the walls, so mould grows. However, not many people realise that additional insulation isn't always the answer. In fact, too much insulation can be the secret cause of mould.

What is the best rigid foam insulation for exterior walls?

The best kind of rigid foam insulation is polyisocyanurate, also known as polyiso. It has the highest R-rating of any rigid foam insulation and comes with a reflective foil on both sides, allowing it to act as a radiant barrier as well.

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.

Does foam board lose R-value over time?

Over the course of time, the R-value drops because the added blowing agents found in the final product eventually is replaced with air making the product less heat resistant. An initially rated R-value 5.0 XPS product will eventually drop to closer to an R-value of 4.3.

Can foam board insulation get rained on?

Insulation boards tend to have good moisture resistant and water repellent qualities. Products such as Celotex and EcoTherm boards for instance have aluminium foil facings on both sides, and a PIR foam that is resistant to water.

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.

Why is foam board insulation so expensive?

Insulation costs vary depending on the materials used. For instance, foam board insulation tends to be pricier than fiberglass or cellulose because it offers a higher R-value and better moisture resistance, impacting both the product cost and the effectiveness in controlling temperature.

Previous article
Is hand sanitizer better than rubbing alcohol?
Next article
What color adds the most value to a home?