A process for preparing nanofoam comprising the following steps: a. providing a mold having a mold cavity defined by mold walls, the mold walls comprising at least three pieces that form a sealed enclosure around the mold cavity while at least one wall is movable with respect the other walls, wherein the three pieces are opposing top plate and bottom plate and side plates oriented such that the side plates extend between the top and bottom plates, the mold further having a sealable port which provides access into the mold cavity when open and seals the mold cavity when shut; b. providing a foamable polymer mixture comprising a polymer and a blowing agent, where the polymer is selected from a group consisting of styrene acrylonitrile copolymers and acrylate polymers, and the foamable polymer mixture is at a temperature and pressure where at the temperature the pressure is at least 690 kilopascals above the pressure needed to fully dissolve the blowing agent in the polymer; c. introducing the foamable polymer mixture into the mold cavity of the mold while maintaining a temperature and pressure where at the temperature the pressure is at least 690 kilopascals above the pressure needed to fully dissolve the blowing agent in the polymer and controlling the pressure by controlling the combined rate of introducing foamable polymer mixture into the mold cavity and movement of a wall of the mold to increase mold cavity volume; and d. releasing the pressure around the foamable polymer mixture by moving at least one piece of the mold wall at a rate of at least 45 centimeters per second so as to increase the volume within the mold thereby causing the foamable polymer mixture to expand into a nanofoam having a porosity of at least 60 percent, a volume of at least 100 cubic centimeters and at least two orthogonal dimensions of four centimeters or more. a. providing a mold having a mold cavity defined by mold walls, the mold walls comprising at least three pieces that form a sealed enclosure around the mold cavity while at least one wall is movable with respect the other walls, wherein the three pieces are opposing top plate and bottom plate and side plates oriented such that the side plates extend between the top and bottom plates, the mold further having a sealable port which provides access into the mold cavity when open and seals the mold cavity when shut; b. providing a foamable polymer mixture comprising a polymer and a blowing agent, where the polymer is selected from a group consisting of styrene acrylonitrile copolymers and acrylate polymers, and the foamable polymer mixture is at a temperature and pressure where at the temperature the pressure is at least 690 kilopascals above the pressure needed to fully dissolve the blowing agent in the polymer; c. introducing the foamable polymer mixture into the mold cavity of the mold while maintaining a temperature and pressure where at the temperature the pressure is at least 690 kilopascals above the pressure needed to fully dissolve the blowing agent in the polymer and controlling the pressure by controlling the combined rate of introducing foamable polymer mixture into the mold cavity and movement of a wall of the mold to increase mold cavity volume; and d. releasing the pressure around the foamable polymer mixture by moving at least one piece of the mold wall at a rate of at least 45 centimeters per second so as to increase the volume within the mold thereby causing the foamable polymer mixture to expand into a nanofoam having a porosity of at least 60 percent, a volume of at least 100 cubic centimeters and at least two orthogonal dimensions of four centimeters or more.