Abstract: A hard head foil cap is provided for foiling hair on an individual, and comprises a head cap provided with a plurality of long narrow slits each having an opening with a width in the range of 1/64? to ¼?. The slits are spaced around the head cap in two or more orientations. Hair shanks may be pulled through the slits for coloring, foiling, highlighting, or bleaching. A hard head foil cap for imparting designs to hair using a head cap with a plurality of long narrow slits spaced around the cap in two or more orientations, the slits configured to form designs to impart the designs in the highlighted hair. A hard head foil cap made by the process of providing an existing, mass manufactured hair cap with a plurality of long narrow slits spaced around the cap in two or more orientations. A method of treating hair.