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Great Stuff Expanding Foam Insulation and Big Gap Filler

Updated on March 6, 2012
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Keith Schroeder writes The Wealthy Accountant blog with 30 years experience in the tax field. He is the tax adviser of Mr. Money Mustache.

Polyurethane foam, commonly called expanding foam insulation, is closed cell foam insulation with high r-value, durability, and ease of use. Expanding foam insulation comes in a slow rise formula for walls and cavities that require low pressure and a fast rise formula for large areas and holes. Fast rise expands 8 to 1. Polyurethane foam is water resistant and soundproof. Whether planning a new home, addition, remodeling, or just plugging the air leaks of an older home, expanding foam insulation is the hands on favorite.

In this article we will discuss the benefits of polyurethane foam, from application, to R-Value, cost, calculating amount needed, and tips to make the project run smooth.


Polyurethane or expanding foam insulation is not the cheapest insulation on the market. When calculating cost, more than the shelf price of the product applied needs to be considered. Foam insulation seals as well as insulates. When airflow is present, other insulations, like fiberglass, are no more than a filter. To illustrate this: think of your furnace filter. Fiberglass and similar non-sealing insulation products do not perform if air flow is present. In most applications there is at least a small amount of air flow. The foundation of most homes are not completely sealed and would benefit from expanding foam insulation in two ways, reduced transfer of air from outside to inside and the insulating properties.

Actual upfront cost depends on the product best for your project. Filling small holes and air leaks can be done for a small amount using cans of expanding foam insulation. Large projects are cheaper per square foot than small projects. Two tank expanding foam insulation kits come in several sizes. The manufacturer will list the square foot, board foot, or cubic foot coverage of the kit. Example: A 200 board foot rated kit will cover about 162 square feet at 1 inch thick for a total yield of 13 cubic feet. This many sound like a large kit, but it is not. Measure out you job size to get an idea of how much expanding foam insulation you will need.

Preparation and Application

Before you begin applying foam insulation you should clean the surface of gross dirt, debris, and oil. Foam insulation sticks to everything except oil. It is still best to remove any accumulation of dirt and debris. A simple sweeping should be sufficient to prep the surface. Oil should be scrubbed free of any surface as the foam will not stick and will pull back as it dries, leaving a small gap in your insulating project. A small gap can undo a large portion of the benefit gained.

It is more than important, it is necessary, to wear protective clothing when applying expanding foam insulation. If you get foam insulation on your hands or face it will NOT wash off.; you will have to wait until it wears off. A painter’s body uniform works well and is low cost and replaceable after a few uses. Gloves and a mask are also necessary. The mask should be the type with filters, not a simple cloth over the mouth. Also wear a hat. You can thank me later.

Calculating Amount Needed

It is important to measure the size of your project in advance. Expanding foam insulation is an excellent insulation and the cost of your project can be reduced if you eliminate waste.

New homes and additions are easier to measure when open and unfinished. The difficult measurements come from old homes. Filling in dead space around a foundation may require an estimate. It is better to estimate on the low side to save cost. If you complete a project and find you need a small amount more, a small kit can be purchased to finish the job. Expanding foam insulation sticks to itself from old to new project very well and will seal completely as if it were done as one job.

Expanding Foam Insulation Installation


Expanding foam insulation has about an R-7 value per square inch. The biggest gains arise from eliminated air flow. The R-value is calculated on the insulation only and does not consider air flow. You can apply foam insulation in any thickness. In some applications it may work best to let one layer harden before adding a second layer. One or two inches of insulation works best each application.

Tips for a Successful Project

Preparation is key to a successful insulating project. Other tips to make the project easier, faster, and more profitable are:

  • Keep tanks warm. To get the rated yield from an expanding foam insulation kit, the temperature of the tanks should be 75-85 degrees F. You can apply foam insulation if it is colder, but the tanks should be warm for best results and maximum coverage. Cold tanks can yield a third to half less than the rated coverage.
  • Prepare the surface before application if dirt has accumulated.
  • Wear protective clothing. I can’t say this enough.
  • Consider applying under floors. If you are able to apply foam insulation in the basement under the first story floor, you can save energy and increase comfort in one stroke.
  • Apply in layers. One or two inches at a time are best, three inches the most. You can apply additional layers later when the first layer is dry.


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You can enjoy all the benefits of expanding foam insulation, from lower energy bills to greater comfort in the home. Planning is a must. By doing it yourself you can keep the cost low with maximum energy savings.

Please share more ideas and tips in the comment section below. Feel free to link or bookmark this article for future reference.


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