A dynamically polarized proton filter was constructed as a low-energy polarizer. Protons in filter material were polarized by a similar method as the one for the polarized proton target used in high energy physics experiments. Filter material was immersed in liquid 4Hem which was cooled by liquid 3He through a heat exchanger from outside. Liquid 3He was removed from the neutron-beam path, since 3He has a very large capture cross section for the neutron. Considerable improvements in intensity and polarization of the neutron beam were achieved.