Raschig rings are a form of random packing and are used in commercial fractional distillation columns to reduce pressure loss. They are small tube cuttings providing a surface for evaporation of the most volatile part in the refluxing distillate, typically 10 mm in diameter and 12 mm long. These can be made from metal, glass, or ceramic. The height of the ring is equal to its diameter. Rings made of copper tube cuttings are superior at fractionating volatile hydrocarbons mixed with water.