For the self-assembly of mesoscopic colloids into 3D opaline lattices via the hydrodynamic flow/physical confinement method, the packing cells had to be patterned and fabricated in a clean room. Here an alternative fabrication method is described that uses replica molding against an elastomeric mold to generate packing cells under normal laboratory conditions. The bottom part of a packing cell is shown schematically in the Figure.