The design of a special accessory for measuring emissivities of materials by means of the heat pipe heater technique is reported. The measuring system consists of a P-E983 IR spectrophotometer, a model 3600 data station and a heat pipe heater. The measuring technique for low emissivities of materials is studied by means of a double tem- perature-measuring technique. The normal spectral emissivity curves of some materials are measured and the factors which will determine the measuring errors are discussed.