The waterproofing of all kinds of underground works and, specifically, tunnels, implies great complexity due to the technical as well as financial importance of their proper construction and to the long term consequences. The numerous factors that need to be taken into account when planning suitable waterproofing, such as they type of terrain, the water conditions, the type of construction, etc. make the choice of materials critical. Over fifty years of experience yielding satisfactory results make synthetic sheets the best option for most underground works. URDIN T is a synthetic waterproofing membrane capable of offering simple solutions for complex problems in any type of tunnel and in civil engineering canals. Adaptable to all types of terrain and easy to install, it guarantees an optimum and lasting result.