All grades can contain a percentage of recycled fiber. This does not significantly affect the physical or optical properties of these papers, except that they may be more dense and heavier for a given roll diameter. All grades are manufactured to conform to customer requirements of cost, print quality and runability. Optical properties are generally defined by brightness, shade and opacity. Most web offset papers are a blend of two types of pulp to provide a paper with a balance of properties and value.
Mechanical pulp provides good opacity but has low brightness and relatively weaker fiber strength.
Chemical pulp provides stronger fibers and higher brightness but has lower opacity. Paper making is a vast and complex process which produces a substrate to very fine tolerances and ever increasing overall quality. To ensure consistent quality, paper mills rigorously test a wide range of properties. Web tension Optimum web tension is fundamental for color quality and improved productivity. It impacts on waste and available press time.