This paper presents a computer-aided conceptual design system for developing product forms. The system integrates a virtual hand, which is manipulated by the designer, with deformable models representing the product forms. Designers can use gestural input and full hand pointing in the system to discover potential new ways for product form design. In the field of industrial design, styling and ergonomics are two important factors that determine a successful product design. Traditionally, designers explore possible concepts by sketching their ideas and then using clay or foam mock-ups to test them during the early phases of product design. With our deformable modeling simulation system, we provide a useful and efficient tool for industrial designers that enable to produce product form proposals efficiently without unnecessary trial and error. Designers can input pre-scanned 3D raw data or a 3D CAD model as an initial prototype. Then, the input model is given the material's elastic property via the construction of a volume-like mass-spring-damping system. The virtual hand in the system constantly changes gestures as the designer manipulates it with a glove-based input device. The product form will be deformed or shaped according to the amount of force exerted by the virtual hand. A mesh smoothing feature called "PN-triangle" is also used to improve the appearance of the deformed model. Finally, a physical prototype with volume and weight is generated using a rapid prototyping machine. Designers can use these mock-ups to conduct further ergonomic evaluations.