Expanding foam is designed to expand and harden upon contact with the air. It usually comes in canisters with spray nozzles, making it easy to apply the foam in a wide variety of situations. Expanding Foam is ideal for filling and sealing awkward gaps, hollows and cavities such as air leaks around window jambs . It shoots liquid foam deep into cavities, creating a long lasting seal, which insulates against heat, sound and moisture. Suitable for inside or outside use and can be easily trimmed and sanded ready to be painted, filled or plastered.