A hydrogel that crumples up like thin slices of potato being cooked to make chips has been developed by Yael Klein and co-workers from the Hebrew University of Jerusalem. The millimeter thick material crumples into a predetermined structure when heated but reverts to its flattened state when cooled in water. The material is a cross-linked elastic hydrogel composed mainly of polymeric N-isopropylacrylamide (NIPA). This material shrinks by driving out water above 33 Celsius. Dilute NIPA gels shrink the most because it contains more water but high NIPA concentrations shrink only a little. By creating a disc with varying concentrations of NIPA across the material, Klein's team created a thin sheet that shrinks a lot in some places but only a little in others forcing it to crumple under the stress of heating. The team suggests the materials could be used in smart applications to make folded objects that form in response to heat, and even pH, light, or the presence of an additive, such as glucose.