Open or closed cell: 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 ideal for 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 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 SPF offers a higher R-value of 6.0 per inch (as compared to open cell’s 3.7 per inch), impact resistance, and a hard, rigid texture which increases the wall racking strength. 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, 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 fits the bill, 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 material requires seeming and can be punctured during application of the drywall. 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.
While these are some general guidelines, each project must be evaluated by its own unique set of requirements, including climate, budget, and performance requirements.
