Merck Millipore S-Pak™ Membrane Filters, PVDF Quantity: 600; Pore size: 0.45um. Merck Millipore S-Pak Membrane Filters, PVDF Individually sealed with a protective blue paper to prevent contact with the film. S-Pak™ Membrane Filters, PVDF are plain, white sterile filters made from hydrophilic Polyvinylidene Fluoride that have been optimized for.