Current state-of-the-art space radiators are too heavy (5-7 kg/m2) and voluminous to be feasible for some future space missions. Accordingly, there is a need for a revolutionary advanced space radiator system. This paper describes an effort to satisfy that need through the development of an unfurlable heat pipe radiating system.The innovative portion of the unfurlable radiator is the pressure envelope: it is a thin, flexible, heat sealable polymer/metal laminate that is vacuum tight. The laminate allows the radiator to be compactly rolled or folded, easily stowed for transit to space and then unfurled to present a large radiating surface.Condensate return to the evaporator is achieved by a combination of capillary pumping via a flexible porous cable wick and the advanced capillary pumped loop methods of entrainment. The mass density of the radiator is 1.76 kg/m2, representing a reduction in mass of at least a factor of 3 over current radiator technology.Feasibility of the concept was demonstrated through the design, fabrication and test of a proof-of-concept heat pipe element. The element was 1-m long and 2.54-cm in diameter. It was tested in a thermal vacuum chamber and shown to reject 25 W while horizontal. Operation in the against gravity orientation was also demonstrated. Methanol was the working fluid.