RAG PAPER
Paper made from stock containing a substantial percentage of rag pulp. The minimum proportion of such pulp required for a paper to be so designated cannot be specified as it varies from country to country.

REAM
A unit of measurement for sheets of paper; normally 500.

REEL UP
The final process in making paper. After passing through the drying cylinders and, if appropriate, the calender rollers, the newly made paper is wound onto a jumbo reel. This is the reel up stage.

REFINER
A machine, usually equipped with discs or with a cone and plug, intended for the treatment of fibrous materials in an aqueous medium to give them some of the properties needed for the manufacture of pulp or paper with the necessary characteristics.

REGISTER MARKS
A set of fine line crosses or other suitable devices added to the original artwork to provide reference points for the subsequent registration of the colors of a set of printed images.

REINFORCED PAPER
Any paper that has been strengthened mechanically by the incorporation of other materials such as plastics, threads, cloth or strips of metal.

RELATIVE HUMIDITY
Quotient of the amount of moisture in air and the amount that would saturate it at the same temperature and pressure, expressed as a percentage.

RETREE PAPER
Paper that has become available as a result of overmaking, side-runs or because it is in some way less than perfect, perhaps non-standard or slightly sub-standard. Although sold without a guarantee, the substance and size tolerances would be expected to conform to industry standards. Often referred to as Clearance Paper.

RICE PAPER
Sometimes a material that has the same appearance and purposes as paper is called "paper." Rice paper is such an example, since it is not paper, but the sliced and flattened pith of a plant that grows in Taiwan. It is used by Chinese artists as a surface for painting.

ROLL COATING
Any method of coating a web of paper in which the coating is applied directly to the paper by transfer from an applicator roll that carries the coating slip upon its surface. The applicator roll may rotate in the same direction as the paper web or in the reverse direction (reverse roll coating).