Solid Unbleached Board also known as SUB.

This is a grade of paperboard

Paperboard

Paperboard is a thick paper based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker than paper. According to ISO standards, paperboard is a paper with a basis weight above 224 g/m2, but there are exceptions. Paperboard can be single...

 which is typically made of unbleached chemical pulp. Most often it comes with two to three layers of mineral or synthetic pigment coating

Coated paper

Coated paper is paper which has been coated by a compound to impart certain qualities to the paper, including weight, surface gloss, smoothness or reduced ink absorbency. Kaolinite or calcium carbonate are used to coat paper for high quality printing used in packaging industry and in magazines...

 on the top and one layer on the reverse side. Recycled fibres are sometimes used to replace the unbleached chemical pulp.

The main end use for this type of board is for packaging of frozen

Frozen food

Freezing food preserves it from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved their game and produce in unheated buildings during the winter season. Freezing food slows down decomposition by turning water to ice, making it...

 or chilled food

Chilled food

Chilled food is prepared food that is stored at refrigeration temperatures, which are at or below . The key requirements for chilled food products are good quality and microbiological safety at the point of consumption...

, beverage carriers, detergent

Detergent

A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

 cereals, shoes, toys

Toys

Toys is a 1992 comedy film directed by Barry Levinson and starring Robin Williams, Michael Gambon, Joan Cusack, Robin Wright, LL Cool J, and introducing Jamie Foxx as Baker. The film failed at the box office at the time of its release, despite its impressive cast and lavish filmmaking. Levinson was...

and others.