All About Closed-Cell Spray Foam
Closed-cell spray foam is a type of polyurethane insulation often used in buildings, appliances, and other applications requiring thermal insulation. It typically comes as a two-part mix, applied through a nozzle, where it expands and solidifies as it enters the space it’s meant to insulate.
This insulation method is fast to apply, highly effective in hard-to-reach places, and stands up well to various environmental conditions. However, once the foam sets, it becomes rigid and dense, which can complicate future changes like adding electrical wiring or pipes, making retrofitting or repairs more difficult.
In this article, we’ll explore the key features and uses of spray-on closed-cell foam.
Characteristics of Closed-Cell Foam
Of the two main types of polyurethane spray foam, closed-cell foam is denser and more widely used. Often referred to as “medium-density” or “two-pound” foam, it consists of tiny bubbles trapped in a polyurethane matrix. Thanks to its unique composition and blowing agents, it provides superior insulation (a higher R-value) compared to other types.
The foam is created by combining two parts during the application: the “A” part (usually methylene diphenyl diisocyanate and polymeric MDI) and the “B” part (containing polyols, catalysts, blowing agents, flame retardants, and surfactants). Closed-cell foam is also water-resistant, making it perfect for areas like wall cavities and even places that are regularly exposed to moisture, such as foundation walls or roof decks. In outdoor applications, it’s important to protect the foam from UV exposure. When applied at a certain thickness, it can even act as its own vapor barrier.
With an R-value between 6-7 per inch, closed-cell foam is a powerful insulator. Its higher density makes it more rigid, which means it’s often underfilled in interior walls to avoid creating issues with drywall installation. While it’s tempting to fill the entire cavity, this can weaken the foam’s vapor barrier, so professionals typically skim it to avoid such problems.
Beyond its insulation properties, closed-cell foam strengthens the surfaces it bonds with, making structures more rigid and protecting against issues like racking. Because of its strong adhesion, it’s crucial to get the mix right during application, ensuring it stays properly attached without shrinking or pulling away as it dries.
One major benefit of closed-cell foam is that it seals out air movement, reducing drafts and keeping indoor temperatures steady. This also helps prevent mold by lowering humidity levels. However, its density and rigidity mean it can transfer noise, though much of the sound in a home travel through walls anyway.
Application Process
Homeowners can find DIY spray foam kits for small jobs, such as filling gaps around window frames or insulating small spaces. These kits range from single-part cans to more complex two-part systems for larger projects like insulating basement walls or garages.
For large-scale jobs or new construction, contractors are typically called in. They use larger, refillable canisters and high-pressure heating systems to apply the foam, often leaving spaces between studs, joists, and rafters only partially filled. Since closed-cell foam needs open stud bays for installation, it’s generally not suitable for retrofitting unless walls are already exposed.
Safety Considerations
When installing spray foam, it’s essential to wear proper protective gear, including respirators. Areas that have been freshly foamed should be avoided by anyone without PPE for at least 24 hours. Once fully cured, the material is safe and can be disposed of like any regular waste.
There are fire-resistant versions of spray foam available, but it’s important to know that burning foam can release toxic fumes. For safety, building codes typically require a thermal or ignition barrier between foam and occupied spaces.
Costs
The cost of closed-cell insulation typically includes both materials and labor since the specialized equipment needed makes them dependent on each other. Closed-cell spray foam tends to be more expensive than other insulation methods, but many homeowners feel the long-term benefits outweigh the higher upfront costs. To save money, some people choose a hybrid approach, using a mix of foam and more affordable insulation materials like fiberglass or mineral wool.
In colder climates, it’s important to be careful when combining different types of insulation, as condensation can form between them unless enough foam is used, or a vapor barrier is installed to prevent moisture buildup.
Additional Considerations
As homes become better insulated, one issue that’s gaining attention is thermal bridging—where heat moves through structural elements like steel or wood from the inside to the outside. While wood is a poor heat conductor, steel is a common problem in modern buildings. Specialized construction techniques are being developed to minimize heat transfer in these situations.
Conclusion
As part of this article, we discussed closed-cell spray-on foams as insulation products in some detail. In order to locate potential suppliers of products or to view specific product details, you can refer to our other guides or visit our Thomas Supplier Discovery Platform for more information on related products. The Spray Polyurethane Foam Alliance has more information about spray-on foams on their website, so you can take a look at that.
