In this paper, we propose a novel fabrication machine called ProtoMold, which uses interactive vacuum forming system for rapid prototyping. ProtoMold combines a dynamical shape-changing surface that consists of 12 × 8 linear actuators and a vacuum forming system. According to the shape of the surface, this system can mold various 2.5 dimensional objects quickly. Another characteristic of this system is that users can reuse molded objects and change their design; by applying tension and heat to a molded object, the object becomes flat and can be molded again. We also designed user several interaction methods for manipulating ProtoMold. In addition to loading predesigned data, the user can control the shape of the pin display directly using gesture input or physical objects. We propose several use scenarios for ProtoMold: changing the design of a plate based on objects placed on it, fabricating a facemask with a printed texture, and fabricating electrical devices with printed electronic circuits. By using this system, we conducted a user test and discuss the known limitations and potential applications of our system.