Open- or closed-cell spray foam: The age old question
While both open-cell and closed-cell spray foam insulation are proven and effective commercial solutions, each product has its own unique set of qualities and is more suited to certain applications. Armed with this knowledge, specifiers can make better educated decisions when it comes to product selection.
A typical 0.5 lb per cubic foot light density open-cell product, like Icynene’s Classic, forms into a soft and flexible, yet air tight seal, and therefore accommodates a building’s normal structural movement and shifting over time. As a vapor permeable application, it supports bi-directional assembly drying and provides better sound absorption than its closed cell counterpart. Open cell is also a lower cost product and uses an eco-friendly water-based blowing agent for application.
Meanwhile, 2.0 lb per cubic foot medium density closed cell spray foam such as Icynene’s MD-C-200, offers a higher R-value* of 6.75 per inch (as compared to open cell’s 3.7 per inch). Furthermore, its low vapor permeance qualifies it as a class II VDR (vapor diffusion retarder), enabling building owners to meet International Code Council building code requirements for vapor retarders where required.
For example, in Marine Zones 4 and 5 and above, ICC codes require Class I (less than 0.1 perms) or Class II (between 0.1 and 1.0 perms) vapor retarders on the interior side of framed walls. While closed cell meets the requirements of Class II vapor retarders, open cell would require a separate vapor retarder.
As a side point regarding open cell, a 6 mil poly vapor retarder is commonly used with fiberglass insulation materials. However, the application of the poly material can be time-consuming since it requires stapling and cannot cover electrical outlets. Consequently, the use of vapor retarder paint directly over the insulation surface is recommended.
Another important rule of thumb for open vs. closed cell is the fact that open cell is limited to interior applications whereas closed cell can be installed on the building’s exterior as well (in many situations).
While these are some general guidelines, each project must be evaluated by its own unique set of requirements, including climate, budget, and performance requirements.
* R means resistance to heat flow. The higher the R-value, the greater the insulating power. Compare insulation R-values before you buy. There are other factors to consider. The amount of insulation you need depends mainly on the climate you live in. Also, your fuel savings from insulation will depend upon the climate, the type and size of your house, the amount of insulation already in your house, and your fuel use patterns and family size. If you buy too much insulation, it will cost you more than what you'll save on fuel. To get the marked R-value, it is essential that this insulation be installed properly.