Abstract The 3D printing is a way of additive manufacturing that allows the creation of sophisticatedly shaped bodies at relatively low cost and in short time span. It is especially useful for rapid manufacturing, including engineering applications such as rapid prototyping. The commonly used fused deposition modelling (FDM) method dispenses filament from heated nozzle positioned in three axes that hardens after exiting the nozzle. This article presents the research focused on the mechanical properties (mainly the basic tensile strength and elastic modulus) of elements printed using the FDM method, made of two distinctive materials: polyethylene terephthalate glycol (PETG) without additions and glass-fiber reinforced PETG. The paper outlines strengths and weaknesses of the materials described and compares the properties of PETG with and without the addition of glass fiber. The gathered data helps to quantify the mechanical properties of parts made of PETG and may also be used for modelling the properties of 3D printed elements.