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What is the Difference between Open-cell and Closed-cell Urethane Foams?

Open-cell foam is soft - like a cushion or the packaging material molded inside a plastic bag to fit a fragile object being shipped.  The cell walls, or surfaces of the bubbles, are broken and air fills all of the spaces in the material.  This makes the foam soft or weak, as if it were made of broken balloons or soft toy rubber balls.  The insulation value of this foam is related to the insulation value of the calm air inside the matrix of broken cells. The densities of open-cell foams are around 1/2 to 3/4 of a pound per cubic foot.

Closed-cell foam has varying degrees of hardness, depending on its density. A normal, closed-cell insulation or flotation urethane is between 2 and 3 pounds per cubic foot. It is strong enough to walk on without major distortion. Most of the cells or bubbles in the foam are not broken; they resemble inflated balloons or soccer balls, piled together in a compact configuration. This makes it strong or rigid because the bubbles are strong enough to take a lot of pressure, like the inflated tires that hold up an automobile. The cells are full of a special gas, selected to make the insulation value of the foam as high as possible.

The advantages of the closed-cell foam compared to open-cell foam include its strength which reduces rack & sheer stress, highest R-value, and greater resistance to the leakage of air or water vapor. The disadvantage of the closed-cell foam is that it is denser, requiring more material, and therefore, more expense. The choice of foam should be based on the requirements for the other characteristics - strength, vapor control, available space, etc.

Both types of foam are commonly used in building applications.  Some are inappropriate in specific applications. For example, you typically would not use open-cell foam below grade or on buildings on or near bodies of water especially in the humid tropical climates where it could absorb water; this would negate its thermal performance because water is a poor insulator compared to air. Closed-cell foam would be a good choice where small framing sizes need the greatest R-value per inch possible.  Basically, the choice depends on the conditions of each installation. We routinely select from a wide variety of foam systems with varying characteristics, depending on the particular requirements of each clients' project.

Polyurethane Foam Properties

The R-value of foam is higher per inch than other types of insulation

•  The R-value of insulation materials is dependent on ambient temperature and wind conditions.  Independent tests show that at 18 degrees F, with a 15 mph wind, the theoretical R-value of urethane foam drops from 19 to 18, while batt insulation drops from 19 to 7.

•  In retrofits with smaller existing framing sizes, this means that buildings can still be insulated to meet current code requirements.

•  In new construction this means that smaller framing sizes (lower lumber costs and larger rooms) can still be insulated to today's energy efficient standards.

•  Plumbing can be installed in outside walls without freezing because only a thin layer of foam is required between pipes and the outside sheathing.

•  This is effective in bays with steel columns, which have a very small space available for insulation between the steel and the sheathing.

Foam is a good air sealant

•  Air leakage is the number one cause of poor building performance. Foam insulated homes out-perform conventionally insulated homes without requiring complicated and labor-intensive air sealing details.

•  Because foam is air tight, it performs better in windy conditions and resists R-value loss.

•  Batt insulation has virtually no air sealing ability and has to rely on other components of a total thermal envelope to maintain performance levels.

•  Air leakage at penetrations creates an environment for condensation.  This affects overall performance and can compromise indoor air quality (bugs, mold, and rot).  Condensation can also lead to premature structural failure in structural framing and sheathing materials.

•  Independent testing shows that urethane insulated buildings can perform as much as ten times better than today's energy standards.


Closed-cell foam has a very low permeance or potential for water vapor to pass through it

•  This provides protection against moisture transport into the insulation with its related potential for condensation.  Vapor that remains on the inside (the warm side) will not come in contact with cold surfaces where the dew point can be reached.

•  Imperfections in the vapor retarder are less critical with closed-cell foams.

•  Indoor humidity levels are more easily maintained at healthy levels if vapor cannot escape during dry winter weather.

Closed-cell Polyurethane foam is not susceptible to damage from short term wet conditions

•  SPF will not be damaged by roof leaks, foundation leaks, or condensation.

•  SPF can be used below grade and in masonry construction and not sustain damage from water penetration.

•  SPF sealants can help to protect structures against wind-driven rain penetration.

Foam bonds to the structure

•  Foam will not compress or settle.

•  Foam adheres to steel decking on flat roof structures providing effective insulation where venting is impossible and there is no framing cavity to support other types of insulation.

Foam can have structural advantages

•  Foam can help to resist wind shear.

•  Foam can serve to reinforce exterior sheathing and windows.

•  Urethane foams are used in structural panels and other composite structures.

•  Foam can be walked on or nailed into without damaging its performance. It can also be washed without damage.


Foam systems perform well for some types of sound control

•  Both open and closed-cell foams provide good sealing against air-borne sound transmission.

•  Both open and closed-cell foams provide good STC ratings against air-borne sound transmission.

•  No low-density insulation materials are effective against structure-borne sound.  Double layer structural systems, resilient structural materials, or massive structures are the best defense against structure-borne sound.

Toxic mold has recently come to the forefront as a major concern among architects, developers, contractors and homeowners. In the past decade, over 9,000 lawsuits related to mold have been filed in the US and Canada . In addition to the rise in mold-related damage liability and litigation issues, the building industry has also taken note of the health risks associated with toxic mold. As a result of the growing public health and remediation costs, the building and science communities have joined forces to promote environmentally friendly, mold-preventing building products like foam insulation.

What is Toxic Mold?

According to microbiologists, there are more than 100, 000 known species of mold and while most are harmless to humans, over three dozen species can be source of severe health problems. Mold growth is caused by moisture-filled air moving into the walls and roof cavities. Inadequate or poor air barrier system installation, a missing or incomplete vapor retarder and high levels of relative humidity also promote mold growth.

Adverse Heath Effects

Airborne mold spores can cause a series of long and short-term health problems which include respiratory problems, skin or eye irritations, headaches and chronic fatigues. Toxic molds are also being researched as possibly having a link to some severe illnesses such as cancer, and cognitive and neurological impairments.

Structural Damage

The most common structural damages of mold formation include rotting of wood and wooden structural framing. It can also cause damage to the existing insulation materials such as fiberglass batt and blown cellulose.

Prevention & Remediation

According to the EPA, once mold has formed and depending on its spread and the damage caused, remediation can be a costly and lengthy process. According to estimates, cost of single abatement can be as much as $40,000. Although the EPA doesn't list any clear guidelines toward mold prevention, mold CAN be prevented. Since mold formation is directly related to moisture and air infiltration, an adequate air barrier and vapor retarder can prevent mold growth. Polyurethane closed-cell foam performs both highly effective air barrier and vapor retarder when used for insulation.