Standard-made membranes are rubber bags designed for equalizing pressures in enclosed heating systems or waterworks. The quality of the used material and its processing fully comply with the appropriate European standards. Flat bag membranes are used for heating pressure expansion containers that have been designed for being used in drinking and service water systems. These membranes are used for equalizing pressures in heating systems. They are installed in a steel container and they separate the gas (nitrogen) and water areas from each other. Production of these membranes is usually manual by the means of connecting (pasting together) butyl foils and pasting various types of rubber flanges and holders. Assortment of these products is very extensive. It consists of approximately 500 different types with volumes of between 100 and 20,000 litres. Rubena is the holder of a certificate that it received based of a certification audit pursuant to the appropriate standard DIN 4807, Part 3, for heating systems, and DIN 4807-5 for drinking water. The mixture used for manufacturing the membranes for drinking water must also comply with the KTW recommendation for DVGW report - W270.