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What is Foam Board Insulation? How it Works and What it’s Made of

foam board insulation | home insulation

What is Foam Board Insulation? How it Works and What it’s Made of Blog Feature
Amanda Ringler

By: Amanda Ringler on August 20th, 2018

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So, your home isn’t as comfortable as you would like it to be, so you’re considering foam board insulation and want to learn more about it.

Foam board insulation can be installed in any open cavities in your existing home, but if you want it in your walls you’re going to need to take the drywall out.

RetroFoam of Michigan has insulated more than 10,000 projects since joining the insulation game back in 2002. We make it our job to be experts in installing injection and spray foam insulation, but also take time to educate ourselves on other materials as part of our efforts to educate homeowners.

Now let’s get into what foam board insulation is, how it works, what it’s made of, and how it is installed.

What is Foam Board Insulation?

Foam board insulation are rigid panels of insulation that are made of either polystyrene, polyisocyanurate, and polyurethane, according to the U.S. Department of Energy.

Foam board can be used to insulate any exposed cavity in your home from the top to the bottom, and even the walls if you are remodeling and the drywall is down. It can also be installed in the open cavities of your pole barn.

Rigid foam board insulation is offered in a variety of thicknesses, lengths, and facings so it can be customized to fit properly for your project. There are even some brands of foam board that have a white foil vapor barrier on each side to keep water from moving through it, which also keeps mold from forming.

How Foam Board Insulation Works?

Foam board insulation provides good thermal resistance and reduce heat conduction through structural elements, such as wood and steel studs, according to the U.S. DOE.

Conduction is the movement of heat through a medium, which means that reduced heat conduction created by foam board insulation can work to keep your home more comfortable if it is installed correctly.

What is R-Value?

In your research you are going to see a lot about R-Value, but don’t let the number fool you as an insulation’s capability to keep your home comfortable is so much more than that.

So what is R-Value?

R-Value is the capacity of an insulating material’s resistance to heat flow. That means the higher the R-Value, the greater the insulating power of the insulation in some cases. While understanding how R-Value works is good to know, it’s not the revered determiner for all things insulation.

What is Foam Board Insulation Made of?

The most common types of material used to make foam board insulation include polystyrene, polyisocyanurate (polyiso), and polyurethane.

Polystyrene is a colorless, transparent thermoplastic, according to the U.S. DOE. It can be molded expanded polystyrene, like foam boards, expanded polystyrene (EPS), and extruded polystyrene (XPS). Both EPS and XPS are made from polystyrene, but EPS is composed of small plastic beads that are fused together, while XPS begins as a molten material that is pressed to form sheets.

Polyisocyanurate is a thermosetting type of plastic, closed cell foam that contains low-conductivity, hydrochlorofluorocarbon-free gas in its cells. Overtime, polyisocyanurate can lose R-Value as some of the low-conductivity gas escapes and air replaces it.

Polyurethane is a foam insulation that can be either open cell or closed cell. Reflective foil placed facing an open-air space can also act as a radiant barrier.

Pros and Cons of Foam Board Insulation

In your research it’s important to really weigh out the pros and cons of any insulation material.

Let’s look at the pros and cons of foam board insulation.


  • Rigid foam board insulation products are made to be water resistant. This will help limit the amount of moisture buildup that can happen in your home, reducing the chances of mold growth.
  • Expanded polystyrene board is the only foam board that doesn’t use HCFCs in its production.
  • The expanded polystyrene board is the cheapest foam board on the market.
  • The installation of foam boards can be a DIY project for the experienced handyman.


  • The joints between sheets and boards must be taped or caulked to prevent airflow into your home.
  • The foam boards must be custom cut to fit the area where it is going to be installed.
  • Expanded polystyrene boards have air bubbles that can stop heat transfer but can collect moisture making it ineffective for preventing mold and mildew growth.
  • Polyisocyanurate foam boards can decrease insulating abilities over time.
  • Rigid foam boards are slightly more expensive than traditional insulation materials used.

Process of Installing Foam Board Insulation

The process to insulate your home with foam board is pretty straight forward.

This is a material that can be done as a DIY project, but you need to make sure you do it correctly or you will continue to have comfort issues.

The foam board must be cut to perfectly fit the cavity where it will be installed. Next you will use tape or caulk to ensure everything is sealed up nice and tight. If you don’t do this, then air will still be able to move around the foam board.

Foam board can be installed on your roof deck, attic floor, exposed walls, rim joist, and exposed basement walls or crawl space.

Does Your Home Need Updated Insulation?

Since you are doing research on insulation materials, you are likely experiencing some signs that the insulation in your home isn’t working the way it should be.

There are more than a dozen signs and symptoms that your home needs updated insulation. To see how many of these symptoms apply to your home, check out our 18 Signs and Symptoms checklist.

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About Amanda Ringler

Amanda previously has worked as a breaking news and crime reporter, TV news producer, and editor in Flint and Detroit. Throughout her career as a journalist, she has won several awards from The Society of Professional Journalists - Detroit Chapter and the Michigan Press Association. As part of the RetroFoam of Michigan family, Amanda uses her experience as a journalist to write content that will help educate homeowners on the benefits of foam insulation. When Amanda isn’t writing, she’s spending time with her husband and rescued huskies. She also loves knitting, making art, cooking, and hosting dinner and a movie night for friends and family.