Closed cell spray foam

All about Closed Cell Spray Foam

The spray-on closed-cell insulating foam is usually sold as a two-part polyurethane material that is often used in buildings, appliances, etc., as a thermal insulation material. The foam is applied by a mixing or application nozzle from a tank and then expands once it enters the system. In general, spray foam insulation has the advantage of being quick to apply, dexterous in difficult to reach places, and generally resilient to a variety of environmental conditions in comparison to other types of insulation.

Spray foam has the disadvantage of being relatively dense and solid once it has cured, so it is difficult to fish electrical cables or pipes through wall cavities once it has cured, adding additional complexity to simple retrofits or repairs. In this article, we will briefly examine the uses and characteristics of spray-on closed-cell foam.

In order to fill a cavity in a wall, a worker applies closed-cell insulating foam.

Characteristics of closed-cell foam

Among the two types of polyurethane spray foam, closed-cell foam insulation is the denser and more common. The industry often refers to this foam as “medium-density” or “two-pound” foam, as it is made up of several bubbles suspended in a polyurethane matrix. The blowing agent is used to create a thermal barrier that is much more effective than air. It has a higher R-value than other forms of insulation because the blowing agent creates a more effective thermal barrier than air.

The foam is made by mixing two parts in the mixing nozzle, the most common of which is the A part – which usually consists of methylene diphenyl diisocyanate (MDI) and polymeric MDI – and the B part, which usually consists of polyols, catalysts, blowing agents, flame retardants, and surfactants.

Due to the fact that closed-cell foam is water-resistant, it can be used for insulation purposes in common areas such as wall cavities, as well as in applications where water is constantly present – such as against foundation walls or on roof decks – and is an excellent insulation material for outdoor applications. In order to protect it from ultraviolet light, roofing installations should be protected. At a certain depth, it creates a vapor barrier on its own.

There is a R-value of 6-7 for closed-cell polyurethane foams per inch. Since closed-cell foam has a higher density than open-cell foam, it is a bit more difficult to work with after curing. It is for this reason that the interior walls of the house are typically underfilled in order to allow them to be hung without any difficulties. In the case of closed-cell foam, insulation values are high enough that filling the entire cavity is seldom necessary, and skimming the surface to flush may weaken the vapor barrier that has been developed in the body.

In addition to adding strength to the surfaces to which closed-cell foam adheres, when it is cured, it assumes a rigid structure and can also be used to shield the surface from racking. If any remodeler happens to overfill a window cavity and has the foam seep out onto new woodwork, then he will be able to attest to the foam’s adhesion to dry, clean wood.

As the foam dries, professionals dial in mix ratios to ensure proper curing and to keep the foam attached to the frame members without shrinking or pulling away as it dries.

There are also many benefits to closed-cell spray foam insulation, including the fact that it is dense enough to prevent air movement, thus preventing drafts and maintaining a steady temperature. As a result of temperature control, mold growth can also be prevented, as humidity levels are lowered, allowing mold to grow. For closed-cell foam to remain resistant, it has to be dense and strong, and when it is fully formed, it resembles solids.

One of the disadvantages of its rigidity is the fact that it can transmit exterior noise into a house’s living area, although much of the sound is transmitted through the walls anyway.

Application process

Spray-on foam kits are available for homeowners and range from single-component foams in small cans for insulating between window frames, filling small voids, etc., to larger two-part systems for insulating basement walls, garages, and the like.

In general, contractors are usually hired to handle large-scale projects as well as new construction. For example, when it comes to insulating building envelopes, they usually use refillable canisters and heating systems in order to disperse the two components under high pressure to partially fill the spaces between the studs, joists, and rafters, respectively. It is generally understood that closed-cell foams require open stud bays in order to be installed and are therefore not particularly suitable for retrofitting unless existing interior walls are already removed beforehand.

Potential dangers

It is imperative that you wear personal protective equipment, or PPE, when you install spray-on foams. Particularly, respirators should be worn. Residents as well as tradespeople without personal protective equipment should normally stay out of recently-foamed areas for 24 hours. The cured material can be disposed of without special precautions and is generally innocuous.

There are a variety of flame-resistant foams available, as well. Foam that is burning can release many toxic vapors, and building codes generally require a thermal and/or ignition barrier between the foam and occupied spaces; there are a wide range of fire-resistant foams available.


Closed-cell insulation costs are generally priced to include labor and materials, as the two are interdependent because of the equipment required to perform the job. Fiberglass and other batt-type insulation can be priced on the basis of time and materials. Generally, closed-cell foam installation will cost more than any other insulation method, and in many instances, quite a bit more.

Many people who choose closed-cell foam indicate that it offers a greater return on investment than open-cell foam. In order to save money, some homeowners opt to combine foam insulation with batt-type or blown-in insulations such as fiberglass or mineral wool in order to lower costs. These systems combine the air-sealing and insulating properties of foam with the more economical batt-type or blown-in insulations.

It is also important to note that in the case of mineral wool batts, you can add a level of sound deadening to the inside walls as well as fire resistance. Those who live in northern climates must be careful with this approach since moisture can condense between these two types of installations unless sufficient foam is applied or a vapor barrier is erected beneath the inside wall to prevent moisture from condensing.

Additional considerations

With buildings becoming more tightly insulated, attention has been directed at the phenomena of thermal bridging, where heat flows toward cold through structural elements that connect to the inside and outside walls. Ashwood is generally a poor conductor, the most concern is directed at structural steel buildings where the steel provides a conduit for heat transfer.

Elaborate methods of construction have been concocted to fight thermal bridging in such buildings, with some of the theory trickling down to residential stick builds. This paper presents a comprehensive study of these paths and what they may mean for future construction.


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.


Click to Call