We introduce MudPad, a system capable of localized active haptic feedback on multitouch screens. We use an array of electromagnets combined with an overlay containing magnetorheological (MR) fluid to actuate a tablet-sized area. As MudPad has a very low reaction time it is able to produce instant multi-point feedback for multitouch input, ranging from static levels of surface softness to a broad set of dynamically changeable textures. Our system does not only convey global confirmative feedback on user input but allows the UI designer to enrich the entire interface with a tactile layer conveying local semantic information. This also allows users to explore the interface haptically.