What type of piping is known for its smooth inner surface, minimizing friction?

The correct choice is PVC (Polyvinyl Chloride) piping. PVC is widely recognized for having a smooth inner surface, which significantly reduces friction as fluids flow through it. This characteristic is crucial because lower friction means less energy is required to move water or other substances through the pipe, leading to greater efficiency in plumbing and drainage systems. Additionally, the smooth interior helps prevent the build-up of residues and blockages over time, further enhancing the longevity and reliability of the piping system.

In comparison, materials like metal may have a rougher surface depending on the manufacturing process, which can lead to increased friction and potential problems with scaling. Rubber is flexible and often used for specific applications, but it does not typically provide the same friction-reducing characteristics as PVC. Concrete pipes can be quite durable for certain uses, but they are usually not as smooth internally, which can lead to higher resistance to fluid flow.