A coalescing agent for facilitating the separation of a non-aqueous phase from an aqueous phase of an aqueous medium, said agent consisting of particles of a polymeric foam material having: an IFD no. of 40 or higher (i.e. at least 40); a BR no. of 35 or higher (at least 35); a SF no. of 1.8 or higher (i.e. at least 1.8) and a density of 42 kg/m3 or less.