A process for forming a precision article by providing a thin sheet (10, 80) of material having front and back surfaces, placing the front surface of the thin sheet (10, 80) of material in contact with a surface of a mandrel, wherein the surface of the mandrel has a surface shape, and comprising the following steps: a) arranging an enclosure around a portion of the thin sheet and at least a portion of the mandrel to form a sealed interior, with a portion of the back surface of the thin sheet interfacing with an external environment; b) forming at least a partial vacuum in the sealed interior to define a pressure differential between the sealed interior and the external environment, thereby causing the thin sheet (10, 80) to substantially conform to the mandrel surface to form a shaped thin sheet (10, 80); c) securing the back side of the thin sheet (10, 80) to a support structure to define the precision article; and d) removing the precision article from the mandrel, wherein the front surface (12, 82) of the shaped thin sheet (10, 80) defines the precision surface of the article, characterized in that the enclosure is made collapsible by a flexible or semi-flexible material that can support a vacuum within the sealed interior, and is made in the form of a collapsible vacuum bag around a portion of the thin sheet (10, 80) and at least a portion of the mandrel to form the sealed interior, with a portion of the back surface of the thin sheet (10, 80) interfacing with the external environment, and that the process is being carried out at a process temperature between room temperature of nominally 20° C and up to 70° C which is below the melting point temperature T P and the glass transition temperature T T of the material that makes up the thin sheet (10, 80) of which the front surface does define the precision surface (12, 82) of said precision article. a) arranging an enclosure around a portion of the thin sheet and at least a portion of the mandrel to form a sealed interior, with a portion of the back surface of the thin sheet interfacing with an external environment; b) forming at least a partial vacuum in the sealed interior to define a pressure differential between the sealed interior and the external environment, thereby causing the thin sheet (10, 80) to substantially conform to the mandrel surface to form a shaped thin sheet (10, 80); c) securing the back side of the thin sheet (10, 80) to a support structure to define the precision article; and d) removing the precision article from the mandrel, wherein the front surface (12, 82) of the shaped thin sheet (10, 80) defines the precision surface of the article, characterized in that the enclosure is made collapsible by a flexible or semi-flexible material that can support a vacuum within the sealed interior, and is made in the form of a collapsible vacuum bag around a portion of the thin sheet (10, 80) and at least a portion of the mandrel to form the sealed interior, with a portion of the back surface of the thin sheet (10, 80) interfacing with the external environment, and that the process is being carried out at a process temperature between room temperature of nominally 20° C and up to 70° C which is below the melting point temperature T P and the glass transition temperature T T of the material that makes up the thin sheet (10, 80) of which the front surface does define the precision surface (12, 82) of said precision article.