K2/D127-A4 is a type of high-performance, waterproof and fireproof air sealant. It is used to seal openings and joints in buildings, including wall and roof joints, door and window frames, or other building components and weatherproofing prior to the application of drywall or other finishing materials. K2/D127-A4 is an advanced, single component, moisture curing, polyurethane based sealant which cures to a tough and flexible, water-resistant rubber. K2/D127-A4 is easy to apply and dries clear, making it suitable for use even on clear surfaces. Designed for superior strength and durability, K2/D127-A4 provides superior adhesion, flexibility, and weatherproofing sealing capabilities to a range of building substrates. It can be used in extreme temperature and weather conditions, and is UV, fungi, and bacteria retardant.