Because of their lightweight and thinness, the thermal behaviour of architectural textile membranes exhibits an extreme responsiveness to variations in external conditions. For this reason, it is argued that the reliable prediction of the thermal environment experienced in a space enclosed by a tensile membrane skin construction would require a detailed modelling of the dynamic thermal behaviour of the textile construction itself. In order to assess the effect that different membrane constructions might have on thermal conditions inside the enclosed space, the thermal behaviour of two full-scale tensile enclosures, with different ventilation strategies and textile skin constructions, is monitored during an extensive period. The monitored data are compared with the environmental control strategy suggested at their design stage. In addition to the full-scale monitoring programme, the thermal response of a double-layer membrane construction is monitored on a test rig under real weather conditions. The observed thermal behaviour of the tensile membrane constructions serves as a basis for the design of a numerical model capable of simulating the thermal response of single and double-layer membrane skin constructions and of predicting their surface temperatures and the solar radiation directed into the space they enclose. The approach is based on a detailed modelling of the radiative and convective heat transfer processes affecting the membrane surfaces. The accuracy of this model is validated against the large set of environmental data monitored in full-scale enclosures and on the test rig. The proposed model is intended to be externally coupled with a flow analysis package in order to predict the thermal environment experienced inside tensile membrane enclosures.