To answer the question posed in the title of this graduate thesis, a number of tasks from different fields had to be resolved: first, select the material and prepare the samples for measurements, second, master the microhardness measurement technique, third, master the holographic interferometry technique with a microscopic setting and finally give an interpretation of the obtained results. The selected material is PLA plastics for which many mechanical properties have not yet been sufficiently explored and is one of the thermoplastics used as a 3D printing material. More recently, 3D printing is experiencing a true blossoming, so measuring the properties of microhardness of a 3D structure made of PLA plastic is of practical interest with many applications. 3D printer available at the Institute of Physics (Forcebook UltraPrint 3D) was used. For microhardness measurement, Leitz microscope and Vickers method were used. How Vickers microhardness of the printed 3D models changes depending on the various print parameters was explored, with a special attention on the infill of models designed for this occasion. Holographic interferometry generally provides an insight into the topography of changes on a surface. In this case, the superposition of the two holograms of the sample surface recorded before and after the indentation results in 3D information in the form of interference lines. By interpreting interferograms, the answer to the question posed in the title of graduate thesis was achieved. In addition to the tables with microhardness values calculated by Vickers method, the following is further established: the indentation is shallow with the piled up material on its edges and sides slightly bent towards the center of the squared pyramid. This qualitative information obtained by holographic interferometry can easily be quantified and thus contribute to new knowledge of the studied material.