Lennox Y8699 – BOSS 33420 Minimal Expansion Polyurethane Expanding Foam is a professional-grade 334 Series window and door foam designed for controlled, low-pressure sealing applications. This 20 oz ready-to-use aerosol polyurethane foam is formulated to seal gaps, cavities, and penetrations while minimizing expansion, helping prevent distortion or bowing of window and door frames when applied correctly.

BOSS 334 Foam provides excellent adhesion to most common construction materials, excluding Teflon, polyethylene (PE), and polypropylene (PP). It delivers strong thermal and acoustic insulation, making it suitable for HVAC, residential, and commercial construction applications where precise sealing and long-term stability are required. The foam offers excellent filling and mounting capacity with no shrinkage or post-expansion, ensuring a durable and reliable seal over time.

Common applications include installing and sealing window and door frames, filling cavities, sealing roof penetrations, connecting insulation materials, improving thermal insulation in cooling systems, and creating soundproofing layers around mechanical components such as motors. The low-pressure formulation reduces the risk of frame deformation, while the foam’s stability supports consistent performance in demanding environments.

BOSS 334 Minimal Expansion Foam is AAMA 812-04 approved, CFC propellant free, and VOC compliant, making it suitable for use in regulated construction and HVAC environments. The aerosol container allows for convenient application on job sites, supporting clean, efficient, and professional results for installers and service technicians.