NASA’s planned advanced space transportation vehicles will benefit from the use of integral/conformal cryogenic propellant tanks which will reduce the launch weight and lower the earth-to-orbit costs considerably. To implement the novel concept of integral/conformal tanks requires developing an equally novel concept in thermal protection materials. Providing insulation against reentry heating and preserving propellant mass can no longer be considered separate problems to be handled by separate materials. A new family of materials, Superthermal Insulation (STI), has been conceived and investigated by NASA’s Ames Research Center to simultaneously provide both thermal protection and cryogenic insulation in a single, integral material.The present paper presents the results of a series of proof-of-concept tests intended to characterize the thermal performance of STI over a range of operational conditions representative of those which will be encountered in use. Thermal conductivity measurements have been made at both lowered pressure and 1 atm at temperatures from 300 K to 850 K, covering both room and elevated temperatures. In addition, the material has been tested under conditions representative of an extreme case flight scenario in a novel test fixture which allows simulated front face reentry heating with simultaneous cryogenic backface cooling within the environment of a 20 MW arc heater.