Hairy composite particles with polymer nanoscale hairs are grown by precipitated cationic living polymerization onto a particle surface. Composition and length of the hairs are tuneable. The hair growth is general following the hp-growth mode. By step polymerization of varied monomers, multiple segmental hairs are achieved onto a particle surface. As an example, the PEG-conjugated PVBC-PDVB@Fe3O4 hairy particle is derived. It is highly effective to capture oil from the aqueous surroundings and easily recycled with a magnet.