Fibril - fine thread-like structure that fibres are composed of. They are often of more than one ply.

Fibrillation - freeing of the fibrils from within the fibre during the beating/refining process.

Filler - material, generally white mineral matter such as china clay or calcium carbonate, which is added to the paper finish to increase opacity, improve flatness and allow a smoother finish to be obtained.

Fine Paper - fibre-based paper which usually contains less than 10% mechanical pulp eg. quality printing and writing paper.

Finish - surface characteristics imparted to paper by mechanical means.

Fluting Medium (A, B, C & E) - these letters define the type of corrugated material in terms of the number of corrugations per unit length and height.

Fluorescent Paper and Board - white base paper or board coated with a mixture of fluorescent pigment and binder, the latter being used to key the former to the surface. The coating is activated by ultraviolet light, either by exposure to ultraviolet lamp or natural daylight.

Formation - what the paper looks like when held up to the light. Paper is made from fibres; when they are uniformly distributed, solid ink coverage will go down smoothly. Poor formation may lead to print mottle.

Freeness - the rate of water drainage from a fibre/water mixture. Decreased by beating to produce a 'wet' stock, i.e. drainage is slow.

Furnish - mixture of fibre and additives used in a particular paper, ie. ingredients and their proportions.