A thermal conductivity apparatus employing the absolute guarded hot plate principle was designed developed and fabricated for the United States Air Force. The primary objective of this instrument is to test honeycomb structures at elevated temperatures. A secondary objective is to test super-alloys, ceramics, and cermets. In general these operational requirements were met with calibration runs on copper to 1800 F and Al2O3 to 3000 F falling within the prescribed accuracy limits. Further thermal conductivity tests have been completed on Rene' 41 Honeycomb, Titanium Alloy Honeycomb, L605 Cobalt Alloy Honeycomb, Stainless Stainless Steel, Rene' 41, and Fused Silica. Thermal conductance tests on Tungsten and Columbium are planned. A detailed discussion is made of instrumentation and materials compatability problems encountered during the testing program.