This paper develops the concept of thermal modernity in order to offer a more detailed understanding of air conditioning and the historical role it has played in transforming urban and built space. An analysis oriented by the insights of Science and Technology Studies stresses how the international ascendancy of air conditioning has been contingent upon certain socio-political forces and cultural changes that occur at the local level. The productive example of Singapore - often referred to as the air-conditioned nation - is given to reveal the entanglements between indoor comfort provision, economic development and post-colonial nation-building. At a broader level, the paper points towards the importance of understanding air conditioning's impact on the spread of international modernism in analytically expansive ways, such that we can more fully appreciate how it has acted to remodel the built environment at different scales and reconfigure indoor and outdoor relationships. © 2015 RIBA Enterprises.