Solid Unbleached Board (SUB) is usually made entirely from unbleached chemical pulp and is brown in colour. For many carton applications the printing surface either has a white pigment coating or a bleached chemical pulp top layer plus coating. It is also known as SUS (Solid Unbleached Sulphate).

The board is used where either a very high strength (puncture, tear, etc.) or good wet strength properties are required. It is also referred to as Carrier Board since in addition to folding cartons it is used for multipack applications in canning and bottling.