A particulate composition comprising particles having a core comprising a hydrophobic polymer within a shell, characterised in that the shell comprises a semi-permeable membrane. Particulate composition can be used for making a stable dispersion of particles uniformly distributed throughout a first hydrophobic liquid, wherein the particles comprise a core within a shell and the core comprises a hydrophobic polymer into has been imbibed a second hydrophobic liquid, Compositions can be used to encapsulate active substances and may be used in sustained release mechanisms.