Abstract: A deformable cap for scalp cooling is provided. The cap contains a cap member obtained by discharging air inside a hollow ball made of flexible material and a plurality of small pieces of high water content hydrogel contained in the cap member. The hydrogel is prepared by casting an aqueous solution of polyvinyl alcohol into a mold, cooling the cast aqueous solution to -10.degree. C. or lower to obtain a cooled frozen mass followed either by thawing the cooled frozen mass and one to seven additional cooling and thawing operations or by partially dehydrating the cooled frozen mass in vacuum.