The Columbus Orbital Facility is being developed as the European laboratory contribution to the United States' led International Space Station programme.The need to exchange thermal mathematical models frequently amongst the Space Station partners for thermal analyses in support of their individual programme milestone, integration and verification activities requires the development of a commonly agreed and effective approach to identify and validate mathematical models and environments. The approach needs to take into account the fact that the partners have different model and software tool requirements and the fact that the models need to be properly tailored to include all the relevant design features. It must also decouple both programmes from the unavoidable design changes they are still undergoing.This problem presents itself for both active and passive thermal interfaces. Only the activities leading to the development of passive thermal interfaces model are described in the paper. PASSIVE THERMAL INTERFACE - The passive thermal interface activities which have been performed with NASA allow to: a) provide ESA with a simplified overall Space Station thermal mathematical model; b) provide NASA with a simplified COF thermal mathematical model; c) identify the best way to control the passive thermal interface between the Agencies. This paper details the activities performed, the results and agreements reached and a brief summary of the future activities which are still deemed necessary to perfect this approach.