ISO trimmed sheet sizes for paper

Most paper is made from cellulose plant fibre obtained from wood, straw and esparto, although hemp, cotton and linen fibres obtained from waste rags and other sources are also used. In Australia, most fine papers are made from wood. It is pulped or broken down into its fibres either by mechanically disintegrating it or by chemical process. The pulp is subjected to various bleaching, digesting and refining processes. Fillers such as white clay or titanium dioxide are added to it to improve the surface and colour of the paper. Size (starch) is also added to stiffen the paper and reduce absorbency.
Paper coatings
Coated papers are graded A1, A2 and A3 in descending order of quality. Coated papers produce a sharper impression than uncoated papers and give much better resolution of halftones and fine detail. During paper-making, a thin layer of pigment (white clay or calcium carbonate), combined with various additives, is applied to the paper's surface. Coatings can be gloss (reflective), suede, satin or dull (low or little reflection), or matt (non-reflective).
Textured papers
Paper may be embossed during paper-making by feeding the sheet between two rollers that impress a pattern into its surface. These patterns are known by the different textures they simulate, for example, linen, leather and felt etc.
Cover stocks
Cover stocks range from heavyweight papers to two-sided boards (with a similar quality of finish on both sides), one-sided boards (with a lower quality finish on the back) and specialty boards. Most are available in white, but boards also come in a wide range of colours. Specialty boards vary widely in texture, colour and strength. Metallic-surfaced boards are also available.
Recycled paper
Recycled paper may be composed entirely of recycled fibres or a blend of recycled and new fibres. Paper made from raw materials, usually wood, is known as 'virgin' fibre paper because it has been made into paper for the first time.
Recycled content could be described as 'post-industrial waste' where paper has been through a manufacturing process and has then been returned to the mill for repulping. It may include residues or by-products from other industries not usually associated with paper-making, or it may comprise offcuts, remainders, spoiled work or 'broke' (spoilage and waste from the paper mill. 'Post-consumer waste' describes paper that has been collected after use and returned for processing.
Most paper mills and distributors identify recycled papers by the percentage of  recycled fibres they contain and their suitability for particular uses. The archival properties of recycled papers depend on the types of waste paper used as the fibre source. If the collected waste paper can be sorted, different grades of papers and boards can be made.