The tendency for fish-scale formation in case of the cold rolled AI-killed low carbon steel sheets is characterized by the hydrogen permeability. In steel exist various traps for hydrogen atoms. Trapping enhances the solubility of hydrogen but decrease the diffusivity. Traps are, for example, dislocations, grain boundaries, boundaries of second phase particles, steel-inclusion interfaces, micro-cavities etc. Traps can be characterized by their nature. A dislocation core is saturable, reversible trap; while voids and cracks are unsaturable reversible traps. According to our experiments the dislocation density to some extent has no effect on the T-H value. The ferrite grain size has no characteristic effect on the hydrogen permeability. The carbides shape and the present of micro-cavities play an important role in the hydrogen permeation.