The paper presents the examination of the degree of compaction of biomass material in the form of straw, depending on the temperature of the compaction process, the diameter of the pressing punch and the humidity of the compacted straw. The series of punch-sleeve assemblies characterized by the variable diameter of both the punch and the sleeve were used in the tests. For each sleeve diameter, a straw sample was compressed with a force suitable to obtain a compressive stress value of 10 MPa in the sample cross section. Each punch-sleeve assembly was adapted for installation on a durometer, for mounting temperature sensors as well as mounting on the surface of a cylindrical sleeve, a coil heater. Wheat-rye straw was used in the research. The performed tests are to constitute guidelines for the construction of compaction machines suitable for the biomass of this type.