FlexPad is a system that enables interaction with highly flexible projected displays using deformation. It captures the detailed pose and deformation of a flexible surface in real-time using depth data from a Kinect camera. This allows for applications like exploring volumetric data by slicing through it or animating virtual paper characters. The system tracks deformation accurately even during folding and steep bending, though it has limitations for very sharp bends or folds. An evaluation found the tracking performs well during realistic tasks and users can easily interact with the flexible displays. Future work could explore touch input, active flexible displays, and programmable smart materials.