The initial object of this investigation was to design and build an apparatus capable of screening insulation materials for use in arctic shelters. A further object was to determine its suitability for determining thermal conductivity. The apparatus comprised a steel heat sink embedded in a 6-in. core of polyurethane foam coated with glassreinforced plastic. The specimen rested upon the heat sink, and a constant temperature bath rested, in turn, on the specimen. A potentiometer was used to measure the temperature of the sink by means of a connecting thermocouple. After calibration, the apparatus was found to be highly accurate in determining thermal conductivity.