To determine the thermal expansion of any material it is first necessary to know the ‘Coefficient of Thermal Expansion’ or ‘Thermal Expansivity’ often expressed as 10-6 per oC. The coefficient for thermal expansion of aluminum is 24×10-6 per oC or 0.24mm per 10oC per M. For a south facing aluminum skinned sign within the UK an expected temperature range of 50oC is considered reasonable. Therefore given a 2.4m sign panel the expected expansion/contraction is (0.24×5)x2.4 = 2.88mm. For further information refer to BSGA Technical Guideline C2.5(c).