This study used the R & D method based upon Borg and Gall's 10 phases of development. This study was intended to develop and investigate the effectiveness of a convertible book as an instructional medium to increase students' critical thinking skills in learning. Support media that is integrated with HOTS is expected to overcome these problems. Higher-Order Thinking Skills (HOTS) is the key for children in facing the 4.0 industrial revolution.
