Dop Smart/Mono/Twin Rautitan link Dop Smart is a type of flexible piping system for hot and cold water supply and for central heating systems. It is made from a patented and corrosion-resistant material called RAUTITAN, which is a combination of stainless steel and polypropylene. The pipes can be bent to fit into tight spaces and are available in a range of sizes. The system also includes fittings, valves, and a range of accessories. Mono and Twin Rautitan pipes are also available, which are more flexible and suitable for use in tight spaces.