It is known that the apparent film flow rate j 0 of superfluid 4 He increases significantly when the container wall is contaminated by a thin layer of solid air. However, its microscopic mechanism has not yet been clarified enough. We have measured j 0 under largely different conditions for the container wall in terms of surface area (0.77–6.15 m 2 ) and surface morphology using sintered silver fine powders (particle size: 0.10 μ m) and porous glass (pore size: 0.5, 1 μ m). We could increase j 0 by more than two orders of magnitude compared to non-treated smooth glass walls, where liquid helium flows down from the bottom of the container as a continuous stream rather than discrete drips. By modeling the surface morphology, we estimated the effective perimeter of the container L eff and calculated the flow rate j ( = j 0 L 0 / L eff ) , where L 0 is the apparent perimeter without considering the microscopic surface structures. The resultant j values for the various containers are constant within a factor of four, suggesting that the enhancement of L eff plays a major role to change j 0 to such a huge extent and that the superfluid critical velocity, v c , does not change appreciably. The measured temperature dependence of j revealed that v c values in our experiments are determined by the vortex depinning model of Schwarz (Phys Rev B 31(9):5782, 1985 . https://doi.org/10.1103/PhysRevB.31.5782 ) with several nm size pinning sites.