https://interestingengineering.com/researchers-develop-3d-printed-foam-that-expands-40-times-its-volume

Researchers have developed a foaming prepolymer resin for lithographic additive manufacturing, which can be expanded after printing to produce parts up to 40× larger than their original volume. This allows for the fabrication of structures significantly larger than the build volume of the 3D printer that produced them.