Vast quantities of energy are consumed in heating and cooling to provide what are now regarded as acceptable standards of thermal comfort. In the UK as in a number of other countries, there is a real danger that responses in anticipation of global warming and climate change - including growing reliance on air-conditioning - will increase energy demand and CO2 emissions even further. This is an appropriate moment to reflect on the history and future of comfort, both as an idea and as a material reality. Based on interviews and discussions with UK policy makers and building practitioners involved in specifying and constructing what will become the indoor environments of the future, four possible scenarios are identified each with different implications for energy and resource consumption. By actively promoting debate about the indoor environment and associated ways of life, it may yet be possible to avoid becoming locked into social and technical trajectories that are ultimately unsustainable. The aim of this paper is to inspire and initiate just such a discussion through demonstrating that comfort is a highly negotiable socio-cultural construct.