Unibond Expanding Foam 300 ml. This 300ml expanding foam from Uni Bond has been specially designed for filling sealing & insulating most building materials. Simply apply & leave for 12 hours to dry. It comes in an easily storable & transportable aerosol & expands to the exact size of the cavity you need filling. If you're using it during redecoration projects it's sandable & paintable making it perfect for giving a smooth professional finish once dried.