Abstract The emissivity property of low infrared emissivity coatings was studied during the thermal ageing. The influence of roughness, surface structure and electrical conductivity on infrared emissivity was systematically investigated. The results of experimental investigation indicate that the infrared emissivity changes with roughness, surface structure and conductivity during thermal ageing. This effect was explained by thermal oxidation of Al particles and polysiloxane degradation in the composite coatings and confirmed by SEM and XRD. Due to the degradation of polysiloxane and oxidation of Al particles, roughness increases, surface structure forms cracks and gaps, and conductivity reduces obviously with different temperature, which leads to significantly increasing emissivity.