An apparatus or method for generating a microfoam, the apparatus comprising a channel having an inlet and an outlet, a source of foamable liquid and pressurised gas arranged to feed into the inlet, wherein the channel is comprised of a spatially oscillating flow channel to provide an oscillating flow direction, the spatially oscillating flow channel oscillating about a bulk flow direction, the spatially oscillating flow channel providing a sequence of planar cross-sections perpendicular to the flow direction, with a sub-sequence of planar cross-sections that are perpendicular to the bulk flow direction in the plane in question, the sub-sequence comprising at least one plane that does not overlap with at least one other plane in the sub-sequence.