Students use concrete manipulatives to form an imperative affiliation between conceptual and procedural knowledge (Balka, 1993). Hence, it is necessary to design specific mathematics manipulatives that focus on different mathematical concepts. Preservice teachers need to know how to make and use manipulatives that stimulate students' thinking as it is a crucial competency, which they will need during their careers. The goal of the present study was to investigate the manipulative material design processes of preservice mathematics teachers. Data were gathered by using interviews and questionnaires to explore how the preservice teachers devise new manipulatives. It was concluded that the preservice mathematics teachers are struggling to develop new ideas for an appropriate manipulative material design. They encountered structural difficulties when they attempted to transform their ideas into concrete models. Moreover, their ideas and designs sometimes can be very different from manipulatives designed by experts.