A continuous fiIter treatment process in which anionic polymer dispersions (latex) are added to common papermaking filler slurries ai ambient temperature and then mixed with water of temperature higher than the glass transition temperature (Tg) of the latex used. To efficiently fix the latex the temperature of the filler/latex mixture must be 30-60° C. higher than ihe Tg of the latex used. The chemical composition of the resin and the type of surfactant used during the emulsion polymerization process of the polymer latex dispersions are important factors for efficiently fixing the latex onto the filler by adding hot water and improving the properties of paper made with the treated filler. Enhanced fixation of anionic latex onto filler using hot water is done in mixing vessels that can control shear and mixing time. The anionic latexes are totally and irreversibly fixed or bound onto the filler particles and the aggregated filler slurry is stable over time. The latex-treated filler slurry can be added to papermaking furnishes at any point prior to the headbox of the paper machine or stored for later use. It can be added to wood-free or wood-containing furnishes commonly used for making fine papers, mechanical pulp papers, and multi-ply paperboards. Filler retention with only slightly reduce sheot strength and sizing performance are improved. Treated calcium carbonate filler is more acid-resistant and, when used in manufacturing mechanical pulp paper under neutral conditions, less acid is needed to control the pH.