Use a half- or full-face respirator fitted with organic-vapor cartridges for polyester resin, gelcoat, MEKP, acetone, and paint solvents, since it is the styrene and solvent vapor you need to filter out. A particulate dust mask does not stop these fumes. Replace the cartridges once you start to smell solvent through the mask, and store the respirator sealed so the cartridges last.