A method for measuring the apparent thermal conductivity of fibrous insulating materials under non-steady-state conditions is presented. The apparatus comprises one specimen and two heat flow transducers.

Equations describing the variation of heat flow as a function of time and position are given. These equations are used to derive thermal transient properties from the heat flux measured on the cold and hot sides of the specimens.

Finally, measurements on a variety of fibrous insulating materials are presented. These measurements show good agreement between the apparent thermal conductivities measured under transient and steady-state conditions. A significant reduction in test times compared to classic measurements with a single heat flow transducer apparatus was obtained.