Spray foam, which improves thermal performance and air sealing, has transformed building insulation. Two main forms of spray foam insulation—open cell and closed cell—dominate the market. Understanding the main distinctions between these two can help choose the best material for any building or restoration project, ensuring long-term efficiency and comfort.
Spray foam insulation is a two-part liquid that rapidly expands and hardens into cellular plastic. It fills gaps, cracks, and irregular spaces with its expansion, creating a seamless, monolithic air and heat barrier. Open and closed cell versions fulfil these primary goals through different cellular topologies, resulting in considerable differences in their attributes and suitable applications. Closed cell foam insulation is preferred for its strength and moisture resistance. The decision between them depends on density, R-value, vapour permeability, and structural properties.
Once cured, open cell spray foam insulation is light, airy, and pliable like a sponge. Its ‘open’ cells are purposefully unencapsulated. This traps air, a poor heat conductor, in the foam structure’s voids, insulating it. Due to its lower density, open cell foam expands up to 100 times its liquid volume, making it ideal for filling big, complex cavities and reaching intricate areas. For internal applications that benefit from flexibility, its forgiving nature permits some building structure movement without cracking.
In comparison, closed cell foam insulation is denser, stiff, and compact. As its name implies, this foam’s cells are entirely enclosed and firmly packed. These sealed cells contain an insulating gas, commonly hydrofluoroolefin (HFO) or a comparable blowing agent, which has a lower heat conductivity than air. The increased heat resistance per unit thickness of closed cell foam insulation compared to open cell is largely due to this gas. In some construction situations, its stiffness helps sustain walls and roofs.
The two types’ thermal resistance (R-value) is a key difference. Per inch of thickness, open cell spray foam insulation has an R-value of 3.5 to 3.7. This is still better than fibreglass or mineral wool, but far lower than closed cell foam insulation. The latter has an excellent R-value of 6.0 to 7.0 per inch, sometimes greater. A thinner layer of closed cell foam insulation can achieve the same or greater thermal performance as a thicker layer of open cell foam, which is important in projects with limited cavity space.
Air sealing is both spray foam types’ main benefit beyond thermal resistance. Open and closed cell foam insulation provide a monolithic air barrier that decreases air leakage, a major heat loss and gain factor in buildings. Spray foam decreases drafts, improves comfort, and maintains indoor temperatures by eliminating uncontrolled air movement. However, closed cell foam insulation’s denser structure makes it more effective in blocking air penetration, typically outperforming open cell in windy or exposed conditions.
Another important factor is vapour permeability. Open-cell spray foam lets moisture vapour pass. In settings where controlled ventilation controls moisture transport, this trait can be useful. Open cell foam cannot be used alone as a vapour barrier. However, closed cell foam insulation is impervious to moisture and vapour, acting as a vapour barrier when thick enough. This makes closed cell foam insulation ideal for basements, crawl spaces and external walls, where moisture infiltration into the building envelope is crucial to preventing mould growth and structural damage.
Water resistance and vapour permeability are linked. Open cell foam absorbs and holds water, which can reduce its insulating efficacy and cause problems if the building assembly doesn’t control moisture. This renders it inappropriate for water contact or high-risk water exposure. In contrast, closed cell foam insulation resists water absorption. Its strong, impermeable construction sheds water, keeping it insulated even in moist situations. For foundations, exterior sheathing, and other areas where water management is a top priority, closed cell foam insulation is a recommended alternative due to its resistance to moisture.
Another advantage of closed cell foam insulation is structural integrity. Its stiffness and density glue wall assemblies and roof decks together with racking strength. This adds structural reinforcement to a building’s wind uplift and lateral force resistance. The softer, more flexible open cell foam provides little structural strengthening, acting only as insulation and air sealing.
Open-cell foam absorbs airborne sound better. Its softer, sponge-like matrix collects and dissipates sound waves, making it ideal for interior walls and floor cavities to reduce room noise. Due to its density, closed cell foam insulation blocks sound, but it doesn’t absorb it as well as open cell, therefore it’s better for wall insulation than room insulation.
Decisions typically depend on cost. In comparison to closed cell foam insulation, open cell spray foam insulation often has a cheaper upfront material cost. It requires less material to cover an area due to its lower density and greater growth rate. However, overall installed cost and long-term advantages must be considered. Due to its greater R-value per inch, closed cell foam insulation may require less material to meet energy performance requirements, mitigating the initial cost difference, especially in projects with limited space. Over the life of the building, closed cell foam insulation’s energy savings and resilience can boost its ROI.
In residential contexts, open cell spray foam is recommended for wall cavities, attic rafters, and floor joists for cost-effectiveness and sound dampening. Its vapour permeability allows moisture to dry out of the wall assembly, which is beneficial in some climates. However, closed cell foam insulation is best for applications requiring high R-value in small areas, moisture resistance, and structural enhancement. These include exterior walls, crawl spaces, basement walls, commercial structures, and metal buildings. In cold or humid areas, its vapour barrier is essential.
Health and environmental factors also matter. Two types of spray foam insulation minimise energy use and a building’s carbon footprint. Modern formulations use lower-GWP blowing agents. Since the chemicals must cure, sufficient ventilation and PPE are needed during installation. After curing, open and closed cell foam insulation are inert. Reliable installers will follow all safety measures to protect residents’ health and safety.
The choice between open cell and closed cell foam insulation is about choosing the best material for a project, not about which is ‘better’. Climate, building design, budget, and performance qualities (thermal resistance, moisture control, structural integrity, sound attenuation) must be considered. Closed cell foam insulation, which provides unmatched durability and efficiency, is typically used for projects requiring high thermal performance, moisture protection, and structural reinforcement.
Finally, spray foam insulation improves energy efficiency and indoor comfort in modern building envelopes. Open cell spray foam provides good air sealing and sound dampening at a low cost, whereas closed cell foam insulation has a higher R-value per inch, better moisture resistance, and structural benefits. Understanding these distinctions and speaking with qualified insulation professionals who can assess your property’s needs is essential to making an informed selection. Property owners can choose a solution that impacts operational expenses and liveability for decades by choosing intelligently.