Insulating your attic is one of the best ways to improve your home’s energy efficiency. For one, it helps keep your home warmer in the winter and cooler in the summer. But there are other benefits, such as reducing noise pollution and protecting your home from moisture damage.

But what kind of insulation should you use? There are two main types of spray foam insulation: open cell and closed cell. So, which one is best for attic insulation?

Here’s a quick overview of these options.

What’s The Difference Between Open Cell vs Closed Cell Spray Foam?

Open cell spray foam is less dense. Plus, it expands to 120 times its size and is lighter than closed cell spray foam. Due to this, it has an R-value of 3.

Meanwhile, closed cell spray foam is denser. It expands to 33 times its size and is heavier than open cell spray foam.

The structure of closed cell spray foam is more rigid, while the structure of open cell spray foam looks like a sponge. Therefore, the latter has room inside each cell and tends to be more flexible and softer.

You can learn more about the differences between both types of spray foams in our detailed guide here.

What Makes Attic Insulation Special?

The attic is an essential part of your house to insulate. It’s the space between the ceiling and roof, where a lot of heat escapes in the winter and where the sun’s heat comes in during the summer.

Attic insulation is different from other types of insulation because it has to handle extreme temperatures. It also needs to resist moisture because the attic is usually the most humid room in the house.

Therefore, attic insulation must be made of materials that can withstand heat and moisture. The most common type of attic insulation is fiberglass, but there are other options, like cellulose and spray foam.

Fiberglass is the most popular type of attic insulation because it’s inexpensive and easy to install. It’s also effective at both insulating and resisting moisture.

Cellulose is another option for attic insulation. It’s made of recycled paper and treated to resist fire and pests. Cellulose is also environmentally friendly.

Spray foam is the most expensive type of attic insulation. But it’s also the most effective. It expands to fill gaps or cracks and forms a tight seal that stops air from leaking in or out.

When choosing a material for attic insulation, you must consider the R-value. It will determine how well the insulation works. The higher the R-value, the better the insulation will keep your home cool in the summer.

R-30, R-38, and R-49 are the best values for attics and ceilings.

Do note that over-insulation is a thing when it comes to attics. In such instances, you want some heat to escape into your attic during the winter. An over-insulated attic can cause ice dams to form on your roof.

If you’re unsure how much insulation you need, it’s best to consult a professional.

Which One Is Used in Attic Insulation More Commonly, Open Cell of Closed Cell Spray Foam?

If installed correctly, both open and closed cell spray foam work exceptionally well as attic insulation. In most cases, the home’s climate and desired R-value will dictate which type is used.

In general, closed cell spray foam is better at creating a tight seal and providing a higher R-value, while open cell spray foam is more affordable and easier to work with.

Here are some factors to consider when choosing the proper insulation for your attic.


Open cell spray foam insulation tends to be less expensive than closed cell spray foam. If cost is a significant factor in your decision, open cell foam may be the better option.

Insulating Value

The R-value measures an insulation’s ability to resist heat flow. For example, closed cell spray foam has a higher R-value than open cell spray foam, so it will better resist heat flow.

Therefore, closed cell spray foam may be the better choice if you live in a climate with extreme temperatures.

Ease of Installation

Open cell spray foam is less dense than closed cell spray foam, so it expands more when applied. That can make it easier to apply in hard-to-reach areas.

If there are plenty of nooks and crannies in your attic, open cell spray foam will work well to cover them. Meanwhile, if your attic has a flat, smooth surface, closed cell spray foam will be easier to apply evenly.

Moisture Permeability

The moisture permeability of insulation refers to how well it resists water vapor. For example, closed cell spray foam has a higher moisture permeability than open cell spray foam, so it’s better at resisting water vapor.

That makes it the better choice for attics in humid climates.

Advantages of Open Cell Foam Insulation in the Attic

When insulating your attic, you have to consider many factors, including cost, R-value, ease of installation, health concerns, and environmental impact. Open cell spray foam insulation meets these requirements.

Better Expansion

Since open cell spray foam expands more than closed cell foam, it can fill in any gaps and cracks in your attic. It results in a better seal which means that your attic will be better insulated.

Lower Cost

The initial cost of open cell spray foam insulation is lower than that of closed cell foam. In addition, open cell foam uses less material, so it costs less to install.

Vapor Permeable

Attics are prone to condensation since they are not well-ventilated. It can lead to mold growth.

Open cell spray foam is vapor permeable, allowing any moisture to escape. That prevents the formation of mold and mildew.

Noise Reduction

If you use your attic for working or exercising, you will appreciate the noise-reduction properties of open cell spray foam. It will make your attic a quieter place.

Disadvantages of Open Cell Foam Insulation in the Attic

Although open cell foam insulation has several advantages, some potential disadvantages should be considered.

Low R-Value

Since open cell foam is less dense than closed cell foam, it has a lower R-value of 3.5-4 per inch. While this is suitable for moderate temperatures, it will not provide as much insulation in very cold or hot climates.

In that case, you’ll have to use closed cell spray foam for insulation.

Moisture Sensitivity

Open cell foam is also more sensitive to moisture than closed cell foam. Therefore, if any moisture is present during installation, it can reduce the R-value of the foam and create a breeding ground for mold.

Can Closed Cell Foam Be Used In the Attic?

As mentioned above, closed cell foam is better for attic insulation in extreme temperatures. It has a higher R-value of 5.0 to 7.0 per inch.

Therefore, it will provide better insulation in both hot and cold climates. Here are some benefits of closed cell foam insulation:

  • Higher R-Value
  • Better insulation in extreme temperatures
  • Reduced air infiltration
  • Mold resistant

But it also has some downsides.

  • Expensive
  • Requires professional installation
  • Doesn’t fill all cavities
  • May shrink in some instances

What Are Alternatives To Spray Foam For Attic Insulation

Besides the open cell vs closed cell spray foam for attic comparison, there are also some other insulation options that you may want to consider.

  • Fiberglass Batt Insulation: Since it’s less expensive and easier to install, fiberglass is a popular choice for insulation. However, it doesn’t have the same R-value as spray foam and is less effective at sealing gaps and air leaks.
  • Mineral Wool: It is made from recycled glass or rock and has a higher R-value than fiberglass. It’s also more fire-resistant. However, it’s more expensive and can be challenging to install.
  • Cellulose: If you’re looking for a more environmentally friendly option, cellulose is made from recycled paper products. It has a similar R-value to fiberglass.

You might want to choose these options over spray foam due to cost or installation concerns. But keep in mind that they may not provide the same level of insulation.


Evan has decades of experience as a project manager for large-scale commercial renovation home-building projects throughout the US. Currently, Evan runs a successful construction management company in Virginia.

Write A Comment