First, the particle packing and porosity were defined using Eqs. (1) and (2), respectively, which are related to the milling and mixing processes to make radiation shielding sheet (milling, mixing, formation, aging and plastic) and are expected to contribute to the shielding rate. The appropriateness of the Mw to Mn ratio was evaluated using Eq. (3), and the mixing process was carried out with a ratio ⩽3 by considering the flexibility and tensile strength of the radiation shielding sheet.