Heat cutter is a tool for processing styrene forms. Since blades of cutters are steal wires, user can freely bend them. We think this operation is intuitive for 3D shape modeling. IGEL virtually realizes the operation of the heat cutters by a sketch input system. IGEL has two different modes, 2D and 3D modes, and users can switch them freely. In 2D mode, users can draw the shapes of cutters freely. In 3D mode, users can cut the styrene forms using their own cutters. Our implementation represents the styrene forms as triangular meshes, and cuts the meshes according to the user’s operation.