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Softwood fibres, commonly from pine, spruce and fir are long (2-3.5mm). Long fibres give the paper/board strength, but are also rough. Hardwood fibres such as eucalyptus and poplar are shorter (1-1.5mm) and although weaker, can provide a smoother surface for printing. Usually a combination of fibre types provides the optimal performance.
Fibres are identified by comparison with a microphotograph of reference fibres and the ratio of the mix of types of fibres is estimated. A weighting factor is then used in the calculations for the ratios of the different fibres.
Quantitative fibre furnish analysis is made in accordance with British standard BS 7463, international standard ISO 9184 and BPBIF PP No.50 by microscopic examination of a dried suspension of fibres.