Abstract: A collapsible material is provided which maintains a predetermined strength and shape until it is heated and increased in temperature to a desired temperature and then can collapse, after a lapse of a predetermined time. The collapsible material of the present invention is characterized by comprising a base formed of a hydrate of a hydraulic material and unexpanded vermiculite particles dispersed in the base. In the collapsible material of the present invention, it is preferable that the hydraulic material is formed of at least one of cement and gypsum and the unexpanded vermiculite particles are contained in an amount of 0.5 to 15 wt %. Also, in the collapsible material of the present invention, it is preferable that ash balloon particles are contained in an amount of 0.5 to 20 wt %. Further, in the collapsible material of the present invention, it is preferable that a coating film formed of a hydrate of the hydraulic material and silica powder is formed on the surface of the base.