Using the engineering design process as a problem-solving tool, students fabricate keychains made out of resin. Since these keychains are prepared from resin, students learn about the history and thermoplastic nature of resins. Students use a silicone mold to temper the thermoplastic resin from its liquid to its solid state in a two-step casting procedure to produce the final product. The final prototype will be portable, compact, lightweight, and able to attach keys that can fit into a pocket or purse. Students also learn about prototypes and how prototypes compare to models. The aim of this activity is for students to design and assemble a functioning, high-fidelity prototype. Creative engineering of new keychains and keyring allows students to explore functions from the structures that they use in daily life.