Usually, the heavier the weight, the thicker and more expensive the paper. Paper thickness is measured in ten thousandths of inches or thousands of millimeters with an instrument called a caliper. In the paper industry, caliper and thickness are synonymous. Caliper matters because copy and printing equipment is set delicately to handle paper of a certain thickness. The machines may jam if the settings are not changed when necessary.
All paper has some moisture content.
Fillers, like clay, improve opacity, brightness, smoothness and finish. Calcium carbonate reduces the acidity, or pH, in paper and thus improves paper lifetime. Alkaline papers, with low pH, are preferred for archival uses. Too much filler, however, can reduce paper strength and bulk and may dust easily in printing and converting equipment. Additives and dyes improve color or brightness.