Disclosed is a three-dimensional modeling apparatus ( 10 ) that builds up three-dimensional objects in a heated build chamber ( 24 ) by dispensing modeling material from a dispensing head ( 14 ) onto a base ( 16 ) in a pattern determined by control signals from a controller ( 140 ). The motion control components ( 18, 20 ) of the apparatus ( 10 ) are external to and thermally isolated from the build chamber ( 24 ). A deformable thermal insulator ( 132 ) forms a ceiling of the building chamber, allowing motion control of the dispensing head ( 14 ) in an x, y plane by an x-y gantry ( 18 ) located outside of and insulated from the build chamber ( 24 ). In the preferred embodiment, a material dispensing outlet ( 66 ) of the dispensing head is inside the chamber. Thermal isolation of the motion control components from the build chamber allows the chamber to be maintained at a high temperature.