The subject of this work is polymers, more specifically thermosets and polyester resins. In construction, new materials are constantly being introduced due to the development of science and new discoveries. Polymers are therefore modern materials that are being used more and more. In this paper, a brief historical overview of the first use of polymers and important discoveries related to production processes and new materials is given. The work includes the basic types of polymers, their disadvantages, advantages and general properties. An important subdivision of polymers is made according to their thermomechanical behaviour, namely elastomers, thermoplastics and thermosets. Thermosets are described in more detail as they are most commonly used as a matrix in the manufacture of fibre-reinforced polymers, with examples of their use in practise. As part of this work, a ring stiffness test was carried out on a glass fibre reinforced polymer (GRP) pipe. The experiment was carried out in accordance with the standard HRN EN 1228:2003 and is part of the quality control of this construction product. The test procedure is described and accompanied by photographs. The average value of the ring stiffness is calculated and should be greater than or equal to the nominal value for this pipe.