Investigations of physical properities of agricultural materials have been carried out in the Institute of Agrophysics of the Polish Academy of Sciences for many years. The investigations allow to deepen the knowledge of physical properties and processes concerning agricultural materials. They focus on mechanical, rheological, optical and thermal properties as well as their changeability during maturing, harvest and post- harvest processing. The studies have been curried out on the following material: grains, seeds, root of plants, fruits, vegetables, stems, pods etc. The general aim of these investigations is creation of better quality of final products (food). The quality improvement is mainly concerned with limitation of the degree of damage during harvesting, storage or other operations. The investi- gations allow also to indicate reasons and sources of damage of plant material. In consequence they resulted in elimi- nation of operations and/or machines the most negatively influenced raw material.