Frequently Asked Questions

The question I am asked most often is should I use Open cell Or Closed cell.

This may be one of the most important pages on the internet if you are interested in spray foam insulation. When it comes time to actually putting the foam product in your home or commercial building, you must identify whether you will use Open cell foam, or Closed cell foam. This makes a big difference in cost, application methods, and performance.

With the open-cell vs. closed-cell issue, there are two major factors to understand and consider. The first is the nature of the foam. With open-cell foam, the tiny cells of the foam are not completely closed. They are broken and air fills the “open” space inside the material. This makes the foam weaker or softer feeling than closed-cell foam. Open-cell foam has an R-value around 3.9 per inch. (some as high as 4.5 per inch)

The advantages of closed-cell foam compared to open-cell foam include its strength, higher R-value, and its greater resistance to the leakage of air or water vapor. The disadvantage of the closed-cell foam is that it is denser, requires more material, and therefore, is more expensive. Even though it has a greater R-value, typically the cost per R is still higher than open-cell foam. The choice of foam can also be based on the requirements for performance or application specific characteristics. Closed-cell foam has an R-value of around 6.9 per inch. (some as high as 7.2 per inch)

Both types of foam are commonly used in most building applications and the choice for which to use can depend on many of the factors discussed above. Some foam is inappropriate in specific applications. For example, you typically would not use open-cell foam below grade or in flotation applications where it could absorb water; this would negate its thermal performance. Water vapor and moisture permeance is an area of great debate and misunderstanding in the insulation market and construction world as a whole. Most building inspectors and other industry “specialists” have very limited knowledge of it. As discussed earlier, closed cell foam has a low vapor perm rating (Less than 1.0 for 1.5” thick) and Open cell foam has a higher rating of around 10 (for 5”). Using generally accepted terms in the industry, closed cell foam is referred to as “vapor semi-impermeable” and open cell foam is referred to as “vapor semi-permeable”. A few points should be made prior to this discussion. First, moisture will move from areas of high pressure to areas of low pressure, which usually means it moves from warm to cold. Second, warm air can hold more moisture than cold air. Thirdly, this country has many different climates, so if you hear an expert from Texas tell you the “correct” way to insulate your home, you may want to consult a local expert. A good insulation solution in Minneapolis isn’t necessarily good for New York and a good solution for Miami isn’t the same as Seattle. The people you consult for building and insulation advice should have a thorough understanding of the local climate and building science. Unfortunately, most people in the industry don’t have this expertise. A IDR representative has the knowledge to make the best recommendation for you.

Any polyurethane foam will hold up well to liquid water relative to other building materials. They are plastics and when they get wet, they dry. Closed cell foam has stellar performance in these situations. In most cases, no significant amount of water will even enter the cell structure of the foam. Once the conditions that cause the water problem are removed and assuming the foam isn’t under water for months on end, the foam will simply dry out and return to action no worse for wear. On the other hand, the structure of open cell foam is not nearly as strong and it will take on water if a leak is bad enough. In the case of a roof leak or wind driven rain, open cell will simply dry out and return to normal once the leak is stopped. However, in the case of a flood that lasts for days on end whereby the foam is submerged, the pressure and weight against the foam will likely damage its cell structure beyond repair. What does all of this tell you? If you live near a creek or other flood prone areas, or if you have an older home with bad basement drainage, you should seriously consider paying the premium for closed cell foam.

The most common reason folks choose closed cell vs open cell is you are getting a vapor barrier, air barrier and thermal barrier all in one. This also provides the highest R-value in the smallest space. This is very important here in New England where most homes have 2×4 walls and 2×6 roof rafters.

While spray foam cannot stop all ice dams it sure has prevented a lot. This is due to the high R-value at the weak points like the connection at the wall plate where the roof meets the wall. This area is typically 4-6 inches at best in most homes. With conventional fiberglass or cellulose you are only going to fit an R14-R21 in these areas which is at best. Most homes are very poorly insulated at these areas. Closed cell spray foam can achieve the highest R-vale possible in these areas and stop all air movement as well from coming in and causing wind washing Wind washing is the movement of unconditioned outside air around or through buildings in such a way as to diminish or nullify the intended thermal performance of the homes insulation. Wind washing can occur in attics that are vented at the soffits. It can also occur in areas of a home where conditioned spaces abut unconditioned space, for example in areas that are cantilevered (i.e., sections that bump out above the foundation) if those areas are not adequately air sealed with complete air barriers to prevent air from flowing through the floor joist cavities connecting the cantilevered area to the rest of the home. Symptoms of wind washing including cold or hot spots along exterior walls, along second-story walls that border attic spaces, over cantilevered floors, and over or along other areas of the home that border unconditioned spaces.

Another important thing to look for is weather or not the foam your choosing is Green Guard Gold approved. The GREENGUARD Gold standard includes health based criteria for additional chemicals and also requires lower total VOC emissions levels to ensure that products are acceptable for use in environments such as schools and healthcare facilities. In addition to limiting emissions of more than 360 VOCs and total chemical emissions, GREENGUARD Gold Certified products must also comply with requirements of the State of California’s Department of Public Health “Standard Method for the Testing and Evaluation of Volatile Organic Chemical Emissions from Indoor Sources Using Environmental Chambers, Version 1.1 (2010)” (also known as California Section 01350).