A soft, flexible, floating solar heater for floating on liquid generally comprises an inflatable central portion and an inflatable outer ring. The central portion is constructed of upper and lower film bonded together at a central peripheral bond such that, upon inflation, the central portion contracts. A vertical band in the outer ring prevents buckling of the ring from inward contraction of the central portion upon inflation of the central portion. A non-inflated spacer ring may be positioned between the central portion and outer ring to disperse contraction forces and reduce the tendency for the outer ring to buckle.