Best Sealant for UPVC Windows

For UPVC windows, choose a sealant that bonds well to plastic frames and the surrounding masonry, trim or render without becoming brittle. Polyurethane sealants are a popular choice where strong adhesion and durability are needed around window frames. They can accommodate normal building movement and help maintain a reliable seal at the frame-to-wall joint.

Hybrid polymer sealants are also useful for UPVC window sealing because they combine flexibility with strong adhesion and are often paintable once cured. This can make them a practical option where the joint needs to be finished neatly against painted reveals, trims or other surrounding surfaces. The right choice depends on whether the seal is internal or external, whether it needs to be painted, and how much movement the joint is likely to experience.

Best Sealant for UPVC Windows Outside

External UPVC window joints face rain, UV exposure and regular temperature changes, so long-term flexibility and weather resistance are usually more important than initial strength alone. For outside window sealing, silicone and hybrid sealants are commonly used because they can form a weather-resistant perimeter seal around the frame.

For exterior use, look for a sealant designed for glazing, perimeter sealing or external weather-sealing applications. Products such as Dowsil 791 Weatherproofing Silicone Sealant are made for external joints and provide resistance to UV exposure and weathering. Also consider cure time, application conditions, colour match and whether the sealant is suitable for the surfaces around the frame, such as brick, render, stone, timber or metal trims.

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A suitable window sealant should provide a durable, flexible and weather-resistant seal that helps reduce air and water ingress. Silicone sealants are commonly used for exterior window sealing because they retain flexibility and cope well with prolonged exposure to rain and sunlight. Hybrid polymer sealants can be a better fit where a paintable finish or broader substrate compatibility is needed.

When choosing a window sealant, think about the application first: interior frame finishing, exterior UPVC perimeter joints, frame-to-brickwork gaps, or joints around render and trims. Matching the product to the surface, movement and finish will give a cleaner result and reduce the need for repeated maintenance. Browse our window and glazing sealants online, or speak to our team if you need help selecting the right product for a specific frame or exterior joint.