When and How to Use Fire-Resistant PU Foam?

Fireproofing is an integral part of a building’s construction and safety. Although no building material or product can be considered completely fireproof, using a combination of high-quality fire-resistant products when building or renovating a structure enhances its safety and resilience against the impact of fire.

Fire-resistant polyurethane (PU) foam is a specialised polyurethane product that has been chemically modified to resist ignition and slow down flame spread. Unlike standard PU foams, these products contain fire-retardant compounds that create an expanding char layer when exposed to high temperatures, limiting oxygen flow to burning areas, reducing smoke production and spread of toxic gas.

Fire-resistant PU foam is a critical component in a building’s passive fire protection and is mostly used in residential, commercial and industrial buildings where fire compartmentation is crucial. For example, heightened fire safety requirements apply for structures such as apartment buildings, office buildings, public service buildings, healthcare facilities, educational buildings, data centres, manufacturing plants and warehouses.

In Penosil product range we have various fire-resistant PU foams like Penosil Fire Rated Gunfoam B1 187. It is a B1 fire-rated gun foam with excellent thermal (0.030 W/m·K) and sound insulation (62 dB) values.

Passive fire protection products must comply with specific fire safety regulations. Penosil Fire Rated Gunfoam B1 187 has undergone third-party testing and certification for fire resistance performance and is safe to use in both residential and commercial applications:

• EN 1366-4 (fire resistance for linear joint seals), fire resistance rating up to EI240 (fire resistant up to 4 hours or 240 minutes, integrity and insulation).
• EN 13501-1 European fire classification: B-s1,d0 (B – combustible material with a very limited contribution to fire spread, s1 – produces very little or no smoke, d0 – does not produce flaming droplets or particles).
• DIN 4102-1 (fire-retardant) B1.

Where should you use fire-resistant PU foams?

• All installation, sealing and filling works within fire-rated structures.
• Installing fire-resistant doors and windows.
• Sealing linear joints in fire-rated walls; gaps between partition walls and structural elements.
• Sealing around service penetrations; cable and pipe penetrations through walls and floors, electrical conduits and cable trays, HVAC ductwork connections, utility line entry points.
• Fire-resistant PU foam is unsuitable for structural load-bearing gaps or joints subject to significant dynamic movement.

The product application process requires careful attention to joint or gap dimensions. Penosil fire-resistant PU foams are tested with joint sizes ranging from 15 mm to 60 mm in width. The general rule is that fireproofing products’ fire resistance properties perform more effectively in smaller joints and openings than in bigger ones. If a product’s fire resistance has been tested with a certain joint width or penetration diameter, one can assume that using this product in a smaller joint will have the same or greater fire resistance. However, the certified fire-resistance properties cannot be guaranteed if the joint is bigger than marked in the test.

For example, a horizontal joint filled with fire-rated PU foam and then covered with fire-resistant hybrid sealant has different fire-resistance properties depending on the joint size. A 15 mm wide joint with a 20 mm sealant layer depth has an EI240 fire resistance rating, while a 40 mm wide joint with a 30 mm sealant layer depth has an EI90 fire resistance rating.

When sealing larger joints, we recommend using a fire-rated straw foam such as Penosil Fire Rated Foam B1 296. Straw foams usually have higher expansion and mechanical strength than gun foams.

How do you correctly use fire-rated PU foams?

• Temperature: Working temperature does affect the final result. Installation outside the recommended temperature and humidity ranges can affect the PU foam performance. For Penosil Fire Rated Gunfoam B1 187, the recommended application temperature range is +5°C to +30°C. For the best results, both the product and the sealed materials should be around room temperature: +20°C.
• Surface preparation: Before filling and sealing the joints or penetrations in a newly built or renovated building, it is important to make sure that the installed surfaces have had time to properly dry and settle and that there is no more loss of volume of the construction elements. Before the PU foam application, make sure the surfaces to be sealed are clean, stable, dry and free from any dust, loose particles and oil residue. Use a vacuum cleaner or a brush to clean deeper joints.
• Humidity: One-component PU foams need humidity to expand and cure. Spray some water mist on the surfaces to help the foam expand, cure faster and have a more uniform structure. Careful! You want to dampen the surface; do not over-wet it, or the foam structure will have too many air bubbles and the fire-resistant properties will not be achieved.
• Gun quality: Use a high-quality professional foam gun for fire-rated PU foam application. The better the gun, the denser and more airtight the foam structure and its fire-resistant properties.
• Application: Shake the can at least 20 times; the foam components need to be well mixed before foam application. Hold the foam can in an upright position with the valve up. Screw the gun onto the can. Hold the foam can adapter in place with your fingers while screwing the gun onto the can. Hold the can upside down when extruding the foam. Extrude some of the initial foam (1–2 s) into a bin bag to get rid of air bubbles and to ensure a uniform foam structure.
• Expansion: Do not overfill the joints, as this can cause deformation or damage to sealed surfaces. Always check on the product label or its technical document for the recommended joint filling percentage. In the case of Penosil Fire Rated Gunfoam B1 187, the joints should be filled to approx. 75%. In larger joints, the PU foam should be applied in several layers and be moistened slightly between each layer.
• Curing: The final curing time of the PU foam largely depends on the air humidity levels and temperature. Do not cut or cover the foam before it has fully cured. Cutting the foam too early will damage the foam’s fireproofing properties. Once the fire-rated PU foam is fully cured, the excess foam can be cut.
• UV exposure: Although in some cases PU foam alone is sufficient as passive fire protection, it is always recommended to cover the foam surface with an opaque material. UV exposure degrades the PU foam structure and if left uncovered, the foam will lose its fireproofing properties. To reinforce the fireproofing properties of the PU foam, we always recommend covering the cut foam surface with a fire-resistant sealant. For sealing movable joints such as window and door joints, and expansion and connection joints, it is preferable to use a sealant with high movement capability such as Penosil FireStop Silicone 331 and Penosil FireStop Hybrid 720. To seal around pipe and cable penetrations, it is recommended to use an intumescent acrylic sealant such as Penosil FireStop Intumescent Acrylic 681 or Penosil FireStop Intumescent Graphite Acrylic 682.
• Maintenance: The condition of fire-resistant joints and penetrations should be monitored on a regular basis. Usually, the assessment of fire-resistant PU foam is included in routine fire safety inspections. The PU foam should be replaced when there is visible damage, gaps or deterioration to the foam structure, the regulatory requirements change, or the manufacturer’s recommended replacement interval has been reached.
• Documentation: Ensure that all installation and repair work records demonstrating proper application methods are kept.

Whether you are sealing fireproof doors in a residential building, protecting service penetrations in a commercial building, or ensuring compartmentation in industrial facilities, a high-quality fire-resistant PU foam represents a critical component in a building’s fire safety and provides an essential barrier against the spread of fire and smoke.

When following proper installation techniques, as well as regulatory and maintenance requirements, these PU foams contribute significantly to passive fire protection systems. As building regulations continue to evolve and fire safety requirements become stricter, the role of fire-resistant PU foams will only grow in importance. Have a look at Penosil Fireproofing Solutions here.