Measure of the evenness or lack of contour of a paper's surface. In terms of basic printability, a surface as free as possible of irregularities is desirable, but smoothness is also a function of the interrelationship of other paper properties, and varies with assorted manufacturing processes. Smoothness tends to be characterized by a wild formation, which is dependent on the degree of fiber refining, the extent of wet pressing, the extent of calendering and supercalendering, the use of coatings, and the desired paper finish. (See Paper and Papermaking: Paper Properties.) Also known as levelness.
A measure of paper smoothness is made using an air leak tester, which determines the time it takes for a volume of air to seep between a smooth glass plate and the paper sample. Smoothness can also be measured using a Bekk Smoothness Tester or a Gurley Smoothness Tester. More rapid measurements can be made with a Sheffield Smoothness Gauge or a Bendtsen Smoothness Tester. All these devices utilize rates of air flow over a paper surface as an indicator of smoothness (although they all do it in different ways).