How a Spray Foam Insulation System Works

Basics

Spray foam insulation is a polyurethane foam that is sprayed onto a surface such as wood, metal or fiberglass as insulation. It is used in homes, commercial buildings, boats and just about anything that needs insulation and a tight, well-sealed air barrier.

It begins as two parts: part A, the catalyst, and part B, the proprietary ingredient that makes each manufacture's brand of foam unique. Each part is pumped through a hose to a gun-like spray head or nozzle. At the nozzle, parts A and B combine and are blown out onto whatever surface is being insulated. At this point, it is thin and wet, but it sticks like fly paper and rapidly expands to about 100 times its original volume.

Benefits

Compared to fiberglass batt insulation, spray foam can save you up to 50 percent on your heating and cooling costs. Because it sticks so well and expands to fill voids, spray foam creates an airtight seal. That means that inside your home, it not only insulates against outside air temperatures, but it also keeps out drafts, pollen and insects that have a way of creeping through gaps and cracks. Spray foam also reduces moisture and the mold that can come along with it. Federal tax credits and state grant programs can pick up the tab for some of the installation costs.

Some Drawbacks

Spray foam can be expensive upfront. It is about twice as expensive as fiberglass insulation, and you can not usually install it yourself unless your project is very small. When you spray it around electrical wires and plumbing, it fills the voids and stays put, making modifications difficult. Fishing wires through a wall is all but impossible, and re-routing plumbing means you have to cut the foam away. (Of course fishing wires through a wall pushes batt insulation out of the way and ruins your thermal protection too, so either way, there are pros and cons.)

Types of Foam

Open-cell spray foam is flexible and is used indoors. It generally has an R-value of between 3.6 and 4 per inch of thickness.

Closed-cell foam is more rigid and waterproof. It has a higher R-value than open cell foam, usually around R-5 or R-6.

How is it Installed

You can buy cans of spray foam at the hardware store and two-part kits online for small do-it-yourself jobs like insulating cracks and around windows and doors. A word of caution---if you're sealing around windows and doors, make sure the product label says "for windows and doors." Otherwise, the foam may expand and become rigid, which makes opening and closing the windows or doors difficult.

For new construction, attics, additions and remodeling, you'll need a professional installer. The pros will come to your house with a truck that has a generator and oil-drum sized cans of spray foam. They should thoroughly mask off any place in the home where they will be. If they have to drag their hoses up your stairway to get to an attic, they will put down plastic and protect any surface that could accidentally come into contact with the foam. Once it sticks, it won't come off. When they spray the foam on bare, un-drywalled walls or attic spaces, some of it will expand beyond the studs. The crew will trim off the excess foam as it cures.

Green Options

The most common type of spray foam is petroleum-based, but there are some greener products out there.

BioBased Technologies has a soy-based open- and closed-cell foam, and another company called Icynene offers a castor-oil based open-cell foam in addition to traditional petroleum products. Many companies also use water-based blowing agents instead of petroleum ones.