An thermally expandable sheet includes a base and a thermal expansion layer arranged on one surface of the base and configured to be used in manufacture of a shaped object by swelling of at least a portion of the thermal expansion layer. The thermal expansion layer includes a first thermally expandable material having a first expansion initiation temperature and a first maximum expansion temperature, and a second thermally expandable material having a second expansion initiation temperature and a second maximum expansion temperature. The first expansion initiation temperature and the second expansion initiation temperature are high in comparison to a temperature of an environment in which the shaped object is to be placed. The second maximum expansion temperature is high in comparison to the first maximum expansion temperature.