This stiffness is controlled by the addition of “sizings,”—fine powder additives, such as kaolin and calcium carbonate, that among other things reduce the paper’s ability to absorb moisture, causing inks to dry on its surface rather than infuse its fibers, while also allowing the whiteness of the paper to be controlled. These powders, and the binders that bond them to the cellulose fibers of the paper, create what’s known as a “composite matrix.”
