Abstract: A method and apparatus for determining the bulk thermal conductivity of a particular material includes the steps of embedding a thermistor in the material for which the bulk thermal conductivity is to be measured, applying a small current from a constant current source to the thermistor, mathematically determining the temperature of the material, applying a larger current to the thermistor until a steady state thermal condition is obtained, calculating the thermistor resistance, and finally calculating the thermal conductivity of the material according to the formula ##STR1## where I is the large current, R is the thermistor resistance when heated by the larger current, r.sub.1 is the radius of the thermistor glass bead, T.sub.1 is the surface temperature of the glass envelope of the thermistor and T.sub.2 is the homogenous temperature of material whose bulk thermal conductivity is to be measured.