Abstract: A solar heat collector of a flexible material is composed of superposed flexible foils joined together along their rims to form a heat collecting chamber therebetween. A flow of heat carrying medium is directed through the collecting chamber. In order to keep the foils in a taut condition, two opposite rim portions of the foils are formed with marginal chambers for accommodating a weight. The bottom foil is supported on an insulating plate with raised opposite lateral walls and the tensioning weights hang over the edges of the lateral walls to tension the foils by the force of gravity. If desired, the clearance between respective foils can be adjusted by the provision of discrete supporting bars of different height.