Polypropylene (PP) is a thermoplastic that belongs to the group of polyolefins, a group of thermoplastics that have specific properties and, unlike other thermoplastics, have a developed yield strength of the material. Some of the most important properties of polypropylene are chemical resistance, elasticity, toughness and fatigue resistance. Glass-reinforced polymer (GRP) is a strong and very versatile material that behaves differently than thermoplastic materials that are commonly used in everyday objects. It is a composite material made of glass fibres that are woven together to create a flexible fabric and the matrix can be made of unsaturated polyester, vinyl ester or epoxy resin. The pipes highlighted in this paper are sewer pipes with different nominal diameters labelled as PP 315, PP 400 and GRP 500 with different values of ring stiffness. In this paper, the properties of individual materials and their application, especially in construction, are investigated in general. Experimental research of the ring stiffness is conducted on pipe samples PP 315 and PP 400 according to the standard HRN EN ISO 9969: 2016 and on a pipe sample GRP 500 according to the standard HRN EN 1228: 2003.