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Spray Foam

Types of Spray Foam | One-Component Spray Foam | Two-Component Spray Foam | Open-Cell Spray Foam | Closed-Cell Spray Foam | Comparison of Open-Cell and Closed-Cell Spray Foam | Applications for Spray Foam Insulation | Unvented Attic Insulation | Crawlspace Insulation | Wall Insulation

Quick Facts

  • Made of expanding polyurethane which is stable, durable, and resists air flow, water, and pest damage
  • Air seals as well as insulates, keeping heat in and stopping conditioned air from escaping from the house
  • Very effective when installed because it eliminates air gaps which compromise insulation value, unlike batt insulation which is usually installed with air gaps
  • More practical to install correctly (compared with batt insulation) in awkward areas such as crawlspace and attic rafters
  • Can add structural strength to a building (closed cell only)
  • Can be used in attic and crawlspace sealing and insulation, which saves energy by bringing ducts and pipes into conditioned space and which is being integrated into new building codes as a proven way to eliminate moisture problems and heat loss

Types of Spray Foam

Different types of spray foam have different properties and are appropriate for different applications.

One-Component Spray Foam

This is the type of expanding foam typically sold in spray cans in home improvement stores.  Canned foam expands to about two to three times its original volume. It is primarily intended to seal gaps and cracks in order to air tighten the building envelope. It can act as a barrier to drafts, insects, and sound, as well as repel moisture.  It is referred to as one component because it only reacts with the moisture in the air; there is no need to mix it with other compounds before applying it.  It takes about 45 minutes to cure (harden).

Although it can have an insulation value (R-3.5 to R-5 per inch) comparable to that of some two-component foam, one-component spray foam is not practical for insulation of large surfaces because 1) it expands very little compared to two-component foam, 2) it is less stable and 3) takes longer to cure.

Available products include:

Two-Component Spray Foam

This type of spray foam is widely used in green building construction of new homes as well as energy efficiency retrofits of existing homes as an insulator and an air sealer. It is uses two components which are mixed during installation and react together to expand up to 100 times their original volume.  This forms millions of tiny bubbles with a gas which has higher insulation value than air.

During installation, two separate components are mixed together and sprayed on to the surface to be insulated using water or another blowing medium.  Two-component spray foam can be either open-cell or closed-cell.

Open-Cell Spray Foam

Open-cell foam expands about 100 times its original volume during application.  It is called open-cell because the bubbles, or cells, in the foam are more open to permeation by the air and because the cell walls are not rigid.  This yields a somewhat spongy foam which is a great air sealer and insulator but which is permeable to water vapor (although it is water resistant). Unlike closed-cell foam, open-cell foam also has great acoustic dampening qualities.

Manufacturers include:

Closed-Cell Spray Foam

Closed-cell foam does not expand as much as open-cell foam during application, resulting in a higher density foam which provides more structural strength and better water vapor protection than open-cell, but which is also more expensive (since more material is needed to cover the same volume).

Manufacturers include:

Comparison of Open-Cell and Closed-Cell Spray Foam

While characteristics vary somewhat, comparing open and closed cell spray foam of the same manufacturer across a few manufacturers yields the following comparison which shows that both foams provide roughly equal amounts of air sealing and that closed-cell foam is about four times as dense and insulates twice as much as open-cell foam.  Closed cell foam also provides vastly more structural strength (tensile resistance) and protection against water vapor.

—— Open-Cell Closed-Cell Fiberglass Batts*
Density (lb/ft 3 ) 0.5 1.7-2.4 0.4-1.6
Insulation (R-value per inch) 3.6-3.8 5.8-6.4 2.6-4.3
Water permeability (perm-inch) 9.3 0.73 completely permeable
Air Permeability (L/s/m 2 ) 0.013 0.013 completely permeable
Tensile Strength (psi) 3-5.2 19-23 none

*Note: for comparison purposes. Sources: biobased.net, Certainteed, Bayer.



Applications for Spray Foam Insulation

Spray foam is widely used in green building projects.  It is quite versatile but has three main applications.

Unvented Attic Insulation

Either in new construction or in energy efficiency retrofitting of existing buildings, it can be advantageous to convert a traditionally vented attic to a sealed attic.  This method has long been considered by the building science community as an improvement for attic insulation and moisture control.  It consists of sealing up all attic vents and applying spray foam to the attic rafters.  This provides double insulation by insulating and air sealing the attic as well as by bringing ducts and pipes into conditioned space.  Heat losses from water pipes and forced air ducts are greatly reduced by protecting these systems from typically extreme attic temperatures.

Open-cell foam works great for this application, except in very cold climates.  In areas with high speed winds such as tornadoes and hurricanes, the added vapor barrier and structural support of closed-cell foam can help keep the roof intact.

Crawlspace Insulation

An unsealed or poorly insulated crawlspacecontributes to the stack effect, where warm inside air rises and exits the house through leaks in the building envelope, pulling in cool, contaminated air infiltrates from the crawlspace.  Applying spray foam (open- or closed-cell) to the overhead rafters in the crawlspace seals against infiltration as well as insulates against heat loss.

In areas with high humidity or high water tables, sealing a crawlspace can reduce moisture problems.  Closed-cell foam would need to be used due to its water vapor retardant properties.  Sump pumps and other drainage systems may also be required.

Wall Insulation

In new construction, spray foam can easily be applied before drywall is installed.  In retrofits of existing homes, a special form of expanding foam can be poured into wall cavities instead of being sprayed.  Alternatively, blown in insulation may be used.

Important Disclaimer
Product examples are for informative purposes only and mention of any product does not constitute a recommendation or endorsement of any product.