Why Is Spray Foam A Good Insulator?

You want good insulation for your new project. You've heard that spray foam insulation is one of the best insulators, but you don't understand why. Is that something people say to justify how much spray foam costs? What makes spray foam such a good insulation product?

South Central Services has insulated hundreds of new and existing homes around Camp Hill, Pennsylvania. It is true that spray foam is an excellent insulating material, and we will explain why in this article.

By the time you’ve finished reading, you’ll understand:

• What spray foam is made of
• How much R-value spray foam offers
• Why spray foam considered a superior insulating material

Don't have time to read right now? Check out everything you need to know at a glance.

Spray Foam Is A Type Of Polyurethane Plastic.

When it comes to stopping heat transfer, material matters. Metal and water are both very conductive materials. Wood, glass, and plastic are less conductive. Insulation must be made of a material with poor conductivity (also known as a high resistance to conductive heat transfer).

Spray foam insulation is a type of plastic, specifically polyurethane. Spray foam is created when two chemical compounds are portioned, heated, atomized, and combined through a chemical reaction. As long as the reaction variables are monitored and controlled, the resulting product of the chemical reaction is plastic polyurethane foam.

Plastic is not a good conductor of heat, which is precisely what you want from insulation. The insulating power of plastic foam is easy to see in our everyday lives. If you've ever held a styrofoam coffee cup, you experienced its insulating properties when the hot coffee didn't burn your hand.

Polyurethane Plastic Has A High R-Value.

All insulations need to resist conductive heat transfer. It's the first thing to look for in a new insulating material. Resistance to conductive heat transfer is so significant that it has its own metric called R-value.

Anytime you research insulation, you'll see R-value advertised. Knowing how much R-value per inch an insulation can deliver is vital. Different areas of a home have different R-value needs. Basements and crawl spaces don't need as much R-value as an attic because attics experience more temperature change (delta T) than other areas of the home.

Building codes determine exactly how much insulation is necessary and what R-value you need. R-value can also vary depending on where you live. In our climate zone, Climate Zone 5, required R-values differ greatly from further south.

Spray foam insulation delivers a high R-value per inch. Open cell spray foam is comparable to blown-in cellulose, with an R-value of R-3.7 per inch. Closed cell spray foam is even more efficient, with an R-value of R-7 per inch. R-values can vary a bit by manufacturer, but as a general rule, these R-values should hold true for spray foam.

Spray-Applied Plastic Has No Seams.

Once R-value has been established, other aspects of insulation materials must be considered. Something that sets spray foam insulation apart is its seamless application. Since it is a spray-applied product, spray foam can adhere anywhere without gaps, cracks, or seams.

This cannot be said of other insulation products, such as batts, blown-in insulation, or foam boards. Batt insulation sags over time and, when installed incorrectly, can have cracks and gaps. Blown-in insulation will settle over time, and foam board has seams even when installed edge-to-edge.

Since spray foam is seamlessly applied, there is no risk of leaving areas open to heat transfer. Spray foam will also not sag, settle, or gap over time. It adheres in place permanently.

Seamless Insulation Makes Effective Barriers At The Right Thickness.

When installed at the right thickness, spray foam insulation offers seamless barriers. Both open cell and closed cell spray foam can create an air barrier. Closed cell spray foam can create a vapor barrier.

1 inch of closed cell and 3.5 inches of open cell is enough insulation to make a seamless airtight seal. An air-seal prevents air leakage, which directly impacts energy efficiency. Air leaks cause expensive, conditioned air to exchange with the air outside. Uncontrolled air leakage must be stopped with an air-seal.

2 inches of closed cell is enough insulation to make a seamless vapor barrier. Vapor barriers stop vapor from passing through your insulation. Vapor transfer is a more complex topic than air leakage. Sometimes, places in a home need to be vapor-permeable.

Climate zones can also impact where a home needs a vapor barrier. However, vapor barriers are essential for applications like basements and crawl spaces. Below-grade spaces deal with excessive moisture and need to control vapor and condensation.

Spray foam must be installed at the right thicknesses to create these barriers, but they are impermeable at the correct depths.

Spray Foam Can Stop All Forms Of Heat Transfer.

Besides stopping air leakage, air barriers also prevent heat transfer.

The traditional measure of insulation performance, the R-value, determines how well a material can resist conductive heat transfer. However, heat can also be transferred through the air via conduction and radiation.

Radiant heat is why you can tell whether or not a burner is hot without burning your hand. Hovering your hand over a hot burner lets you feel the heat transferring through the air. Convection heat transfer refers to how heat travels through your home in the air. Hot air rises, cool air sinks, and heat is also drawn to cold.

By stopping air leakage and air transfer, spray foam also stops heat transfer. Air-sealing is a more modern approach to insulation, and most insulation products cannot offer an airtight seal on their own.

For example, blown-in insulation has a reasonable R-value but doesn't create an airtight seal. At South Central Services, we apply an air-sealing product on attic floors before installing blown-in. That way, a home can benefit from stopping all forms of heat transfer.

The benefit of spray foam is stopping all forms of heat transfer with just one product. An attic with an airtight seal stops conductive heat, radiant heat, and convection heat. Hot air cannot press through the attic in the summer or escape in the winter.

The Bottom Line About Why Spray Foam Insulates So Well

Spray foam insulation is known as a premium product for a reason. Spray foam is a polyurethane foam that resists conductive heat transfer well. This is represented by the high R-values of spray foam insulation. Spray foam also has a seamless application and the possibility for an airtight seal. When applied correctly, spray foam can stop more heat transfer than other insulations with equally good R-values.

Now that you understand why spray foam is a good insulator, your next step is to:

• Discover how long spray foam is supposed to last in your home
• Estimate the cost of spray foam insulation for your project
• Compare open cell and closed cell spray foam insulation