First off, Tommy Lee Wallace changed the color of the mask’s hair. By using a spray paint, Captain Kirk’s blonde locks are transformed into The Shape’s messy dark mane of hair. He also removes the mask’s side burns and eyebrows, to create a less human appearance. Additionally, Wallace cut the eye holes to make them larger. Finally, the mask is sprayed in “appliance white” paint, which creates the creepy pale skin of Halloween‘s villain. Adorably enough, the mask rocks a shower cap during this last part, as to not accidentally paint the hair white.
Article source: https://www.cinemablend.com/news/2495771/see-how-halloweens-mask-is-created-for-michael-myers