The efficient dryer design and the optimization of existing drying processes require both effective drying models and hygrothermal properties. Following extensive research during the previous decades, today's existing models for the drying process are mostly adequate. Thus.most of the requirements for appropriate process design and operation depend on the existence of data for the various properties. The correct estimation of properties is of fundamental importance for the design.optimization and control of the process. The existing knowledge is adequate regarding the hygrothermal properties of the drying medium (air). Most of the efforts should address the problem of finding and standardizing appropriate measuring techniques and selecting and compiling the existing data, concerning hygrothermal and quality properties of the product being dried. The article identifies those areas, where adequate data not exist and future research is needed or data banks should be created.