Open-Cell Vs. Closed-Cell: Which Works Best For Your Insulation Needs?

Whether you're building a new home or in the process of renovating, there comes a point when you need to think about your home's insulation. Spray foam insulation is often used in place of more traditional materials, mostly for its remarkable performance when compared to traditional insulation types.

There are two types of spray foam insulation: open-cell and closed-cell. The following explains the differences between the two and their ideal applications, giving you a better idea of which one works best for your home's insulation needs.

Getting Down to the Basics

According to Fine Homebuilding, open-cell spray foam offers a density of approximately 1/2-pound per cubic foot, while closed-cell spray foam has a density of 2 pounds per cubic foot. Heavier-density spray foams tend to have higher R-values, which is something that should be kept in mind as you choose between open and closed-cell foams.

The reason for this lies with how closed-cell and open-cell foam is constructed. The tiny cells within closed-cell foam are already filled with a dense gas that's also used as a blowing agent. This makes closed-cell spray foam more effective as an air and moisture barrier.

With open-cell foam, the tiny cells within the foam aren't completely closed, allowing air to rush into the open spaces. This makes open-cell foam feel lighter and weaker than its closed-cell counterpart, which explains the lower density of the foam itself. However, this allows open-cell foams to readily expand and fill as much available space as possible.

Closed-Cell Pros and Cons

Closed-cell spray foam's tightly-packed cell construction offers the best performance of the two spray foam insulation types. Not only is it largely impervious to moisture, it's also a highly effective air barrier. Closed-cell spray foam's density and adhesion properties allow it to provide additional structural strength to its surroundings.

Closed-cell spray foam has one rather noticeable drawback, however. It relies on a hydrofluorocarbon (HFC) as its blowing agent, making it a non-starter for green, eco-friendly projects. Another major drawback to closed-cell spray foam is its cost. In most cases, it costs up to $1 per board foot to install closed-cell spray foam, according to recent figures from CostOwl.

Open-Cell Pros and Cons

At approximately $0.70 per board foot, open-cell spray foam is noticeably cheaper than its closed-cell counterpart. It's also environmentally friendlier than most closed-cell foam sprays. Some open-cell spray foams are actually made from soybean oils and other green materials. Open-cell foams also use carbon dioxide or water as a blowing agent, in contrast to the HFCs commonly used in closed-cell foams.

In spite of these advantages, open-cell spray foams lack the effectiveness of their closed-cell counterparts when it comes to blocking water vapor. In fact, the sponge-like composition of open-cell foam makes it more prone to absorbing and holding moisture than closed-cell foam. This makes open-cell spray foam a better fit for applications that won't come into contact with large amounts of moisture, such as interior wall insulation.

Which Should You Choose?

The type of spray foam insulation that you choose from a place like J & G urethanes spray foam generally depends on the application at hand. Open-cell spray foam is ideal for insulating interior walls thanks to its ability to reduce sound while remaining an effective air barrier. However, it does not do well when it comes to blocking water vapor. In some cases, it's best to pair open-cell spray foam with a vapor-retarding paint for maximum protection.

When it comes to outdoor-facing applications, such as roofing and exterior wall insulation, closed-cell spray foam is the better choice. The denser and more compact cell structure does a better job as a water vapor barrier.