One method employed to measure drying kinetics for small particles is the thin layer method (TLM). In this method, the drying rate of a layer of particles is measured and the single particle kinetics must then be extracted from this data. This scale down process is rather complex since the gas phase changes through the bed which means that the drying conditions vary both in space and time. This paper is essentially a theoretical evaluation of the method. The validity of some of the assumptions made in the scale-down model (e.g. about transfer coefficients and the omission of the heat balance) are tested. Different expected problems such as the effects of the number of transfer units (NTU) and the degree of complexity of the internal drying kinetics on the quality of the results are also addressed.