If exposure to municipal wastewater is a factor, then a group 3 (DIN 18 820 T1) or type 1140 (DIN 16 946 T2) is generally used. For aggressive industrial wastewater, e.g. containing alkaline solutions and/or with high temperatures, the GFRP composite is impregnated with a special vinyl ester resin. This resin corresponds to group 5 in accordance with DIN 18 820 T1 and type 1310 in accordance with DIN 160946 T2. Both resins are compliant with the international standard DIN EN 13121. The polyester resin is categorised as group 4, the vinyl ester resin as group 7a.