A new flow cell system we have designed for thin film samples is used to measure the streaming potential between two parallel films of a polyurethane (PU)/polyvinyl chloride (PVC) blend, and the ζ-potential of PU/PVC blend dope-coated nylon fabrics is then estimated. Furthermore, we propose a novel streaming potential method to directly measure coated films on the inside of the cell lid and the cell body. The ζ-potential of PVC-rich (hydrophobic) surfaces has a lower value than that of PU-rich (hydrophilic) surfaces.