Polarized 3 He neutron spin filters are suitable devices for polarizing neutrons at spallation neutron facilities because of the wide coverage in energy range and the large solid-angles. The glass cell plays an important role in the 3 He spin filters. In order to get good quality of glass cells, the investigation on the microscopic structure would be helpful. In this paper, we report on the results of X-ray diffraction for several glasses. We observed a correlation between the position of the first peak and the helium permeation velocity. We also observed a small difference in the diffraction curve among GE180 glasses with different thermal treatment. Desirable structure for 3 He spin filters is discussed.