DOWSIL DEFENDAIR 200C Air and Weather Barrier 5-Gallon

DOWSIL DEFENDAIR 200C is a water-based, vapor-permeable silicone air and weather barrier coating engineered to protect commercial and institutional buildings from air infiltration and water penetration while allowing trapped vapor to escape. This fluid-applied, elastomeric coating forms a seamless, flexible membrane that maintains its integrity under thermal movement and extreme weather conditions.

The coating’s vapor-permeable design lets interior moisture escape while preventing bulk water intrusion, helping walls stay dry, durable, and energy efficient. DOWSIL DEFENDAIR 200C meets ABAA S0008 performance requirements and features NFPA Class A fire resistance, low VOC emissions, and long-term UV durability. It resists cracking, splitting, and surface degradation even after prolonged exposure to sunlight, rain, and temperature fluctuations from -20 °F (-29 °C) to 300 °F (149 °C).

Designed for both new construction and renovation, DEFENDAIR 200C can be applied by roller or spray, forming a continuous 15 to 17 mil (0.38–0.43 mm) dry-film barrier. It adheres strongly to common substrates such as gypsum sheathing, CMU, OSB, and plywood without sagging or blistering. Once cured, it provides lasting protection and stability behind cladding systems, curtain walls, and masonry veneers.

Backed by Dow’s building-science expertise, DEFENDAIR 200C offers a high-performance, environmentally responsible solution for architects and contractors seeking to enhance envelope integrity and extend the service life of the structure.