The paper discusses some problems related to the guarded hot plate (GHP) and heat flow meter (HFM) apparatus that justify today research efforts and future research programs. For the GHP these include the problem of imbalance detection and its correlation with the metering area definition, the problem of gap width, and the problem of apparatus speed. Also discussed are the specimen-related issues involved in measurements on rigid, highly conductive materials and mass transfer within the specimen during tests.

For the HFM apparatus the different configurations are surveyed, and the effect of the HFM temperature uniformity and its possible correlation with the HFM thermopile layout are discussed.

In conclusion a concise account is given of the activity within the International Organization for Standardization's Technical Committee 163 on Thermal Insulation in its development of international documents for the two test methods.