Details of theoretical and experimental studies of the change in vacuum pressure within a vacuum glazing after extreme thermal cycling are presented. The vacuum glazing was fabricated at low temperature using an indium-copper-indium edge seal. It comprised two 4 mill thick 0.4 m by 0.4 in glass panes with low-emittance coatings separated by an array of stainless steel Support pillars spaced at 25 mm with a diameter of 0.4 mm and a height of 0.15 mm. Thermal cycling tests were undertaken in which the air temperature oil one side of the sample was taken from -30 degrees C to +50 degrees C and back to -30 degrees C 15 times while maintaining an air temperature of 22 degrees C on the other side. After this test procedure, it was found that the glass to glass heat conductance at the centre glazing area, had increased by 10.1% from which the vacuum pressure within the evacuated space was determined to have increased from the negligible level of less than 0.1 Pa to 0.16 Pa using the model of Corrucini. Previous research has shown that if the vacuum pressure is less than 0.1 Pa, the effect of conduction through the residual gas on the total glazing heat transfer is negligible. The degradation of vacuum level determined was corroborated by the change in glass surface temperatures. (C) 2009 Elsevier Ltd. All rights reserved.