Flat evacuated glazing consists of two plane glass panes separated by a narrow internal evacuated space. Separation in the space is maintained by an array of support pillars typically 0.32 mm in diameter and 0.12 mm high arranged on a regular square grid with an inter-pillar separation of up to 40 mm. A detailed three-dimensional finite volume model has been employed to determine the variation of thermal performance of an evacuated glazing as a function of glass pane thickness. It was predicted that for evacuated glazing of dimensions of 0.3 m by 0.3 m and 0.5 m by 0.5 m, reducing glass pane thickness gave improved thermal performance. For evacuated glazings with dimensions of 1 m by 1 m, the opposite was predicted. (c) 2006 Elsevier Ltd. All rights reserved.