Abstract: An inflatable collector for solar energy is provided in which superposed layers of plastic sheet material are heat sealed to one another to provide a pair of layers providing an absorber unit in which the upper layer is pigmented to absorb solar radiation and the pair of layers are sealed to one another in a pattern providing a continuous elongated path. Fluid is supplied to one end of this elongated path and at least one transparent layer is provided overlying the pair of layers, to provide a return space above the pair of layers, and valve means are provided to interconnect the end of the elongated path remote from the fluid supply end with the return space so that fluid heated in the elongated path is further heated in the return space before being withdrawn from the collector.