The invention relates to a process for regulating the porosity and printing properties of paper, in particular uncoated wood-containing paper such as SC-paper, wherein a sufficient quantity of colloidal PCC having a BET surface area of 10-100 m.sup.2/g is used as a filler in the paper to achieve a desired porosity of the paper; as well as paper containing colloidal PCC as filler, and a pigment mixture suitable for paper manufacture and containing colloidal PCC.