Air-leak testers such as Parker Print-Surf, Bendtsen and Sheffield press a ring against the sheet and measure how much air escapes through surface hollows; more flow means a rougher sheet. Print-Surf readings are given in micrometers of roughness under printing-like pressure, so a lower number is smoother. Smoothness governs ink contact, dot quality and gloss, and it is raised by calendering and coating.
PPS roughness came in at 1.1 on the felt side and 1.6 on the wire side, so the press is going to see it.
Readings from different air-leak instruments do not convert reliably, so a smoothness spec must name the method.
Related terms
Calender
Stack of hard rolls that presses a paper web to make it smoother, glossier and more even in thickness.
Coat weight
Mass of dry coating applied to paper per unit area, usually stated per side in grams per square meter.
Two-sidedness
Difference in properties between the two faces of a paper sheet, such as color, brightness, gloss or texture.
Ink holdout
The ability of a paper surface to keep ink and its vehicle on top instead of absorbing them.