Water Absorption (Closed Cell vs. Common Building products)
Closed-cell spray foam is considered highly water-resistant because of its dense closed molecular structure. Unlike open-cell insulation, which contains interconnected air pockets that can absorb and retain moisture like a sponge, closed-cell foam is made up of millions of tiny sealed cells that dramatically limit water penetration. Huntsman products such as
ICYNENE® HFO 200 and FOAM-LOK 2000-3G are specifically engineered to function not only as insulation, but also as an air barrier, vapor retarder, and moisture-resistant barrier. Independent ASTM testing shows Huntsman closed-cell foam can have water absorption as low as 0.3% by volume under ASTM D2842 testing conditions, which is exceptionally low for a building material.
To put that into perspective, many materials commonly perceived as “waterproof” actually absorb more moisture over time than high-quality closed-cell spray foam. The tested ASTM D 2842 (Water absorptions by Volume %) products such as; Asphalt Shingles, fiber cement siding, fiberglass matt insulation, Rockwool insulation all absorb substantially more water than closed-cell foam when exposed to prolonged moisture. Closed-cell spray foam’s absorption rate of roughly 0.3%–1% by volume is comparable to or better than many rigid foam board insulations and significantly lower than any ulterior insulation products that can absorb several times their weight in moisture.
Another reason Huntsman closed-cell foam performs so well around moisture is that it forms a continuous monolithic barrier directly bonded to the substrate. Traditional insulation systems often contain seams, gaps, fastener penetrations, or overlapping layers where moisture and humid air can travel. Spray foam eliminates these pathways by expanding into cracks and fully adhering to wood, masonry, concrete, and metal surfaces. Huntsman closed-cell products also achieve very low vapor permeance ratings — around 0.91 perms at 1 inch thickness in some systems — meaning they greatly restrict moisture vapor transmission through assemblies.
This moisture resistance is one reason certain Huntsman closed-cell foams meet FEMA flood-resistant material classifications for use in areas exposed to water intrusion or flooding. Even after exposure to moisture, properly installed closed-cell foam typically retains its structural integrity and insulating performance far better than fiberglass, cellulose, or open-cell foam, which can trap water and lose effectiveness.
Closed-Cell Foam
Asphalt Shingles
Fiberglass
Fiber-cement siding
MOLD-PROOF
Because polyurethane foam is an inorganic plastic material, mold cannot digest or eat the foam.
Mold requires an organic food source to grow, such as wood, paper, or drywall. Over time, organic dust, pet dander, skin cells, and fabric fibers can settle on the surface of the closed-cell foam. If high humidity or a water leak introduces moisture onto this dusty layer, mold will grow on top of the dust accumulation, using the foam merely as a physical shelf.
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Rockwool (Mineral Wool): Considered 0% likely to act as a primary food source for mold. It is inorganic and hydrophobic, meaning it repels water rather than absorbing it, allowing it to dry without supporting mold growth.
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Fiberglass: Highly resistant to mold (often rated similarly to rockwool in dryness), but it can collect dust and organic particles in its fibers, which can support mold growth if trapped moisture is present.
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Blown-in Cellulose: While treated with borates to inhibit mold growth (often 10–20% of the mixture), it is paper-based. If saturated and maintained in damp conditions, its mold-prevention effectiveness can drop significantly, making it more likely to mold than inorganic alternatives
Structural Strength
High-density closed-cell Spray Polyurethane Foam (SPF) does far more than provide insulation — it also significantly enhances the structural integrity of a building. When properly installed, closed-cell SPF adheres directly to wall studs, exterior sheathing, concrete, and metal framing, creating a continuous bonded assembly that increases rigidity and reinforces the overall structure.
Unlike traditional insulation materials that simply fill cavities, closed-cell foam acts as a structural bonding agent, helping walls resist vibrations, buckling, and shear forces while dramatically improving racking strength by as much as 300–400% according to industry testing. Its dense composition also improves wind uplift resistance in both walls and roofing systems, making structures more capable of withstanding high wind loads and severe weather conditions.
In roofing applications, closed-cell SPF delivers impressive compression strength — typically around 40–50 pounds per square inch — adding durability and support under load. These structural benefits make it especially valuable for post-frame buildings, ready-to-move structures, and tiny homes where added rigidity is critical. While closed-cell spray foam can strengthen assemblies enough to reduce certain interior sheathing requirements in some engineered designs, it is important to understand that it is not a direct replacement for structural framing or load-bearing beams. Additionally, these structural advantages are unique to high-density closed-cell foam; open-cell spray foam remains flexible and is designed primarily for thermal and acoustic insulation rather than structural reinforcement.
