The invention concerns an aqueous slurry comprising thermally expandable microspheres comprising a thermoplastic polymer shell and a propellant entrapped therein, said slurry further comprising an at least partially water soluble polymer selected from the group consisting of gums, celluloses, chitins, chitosans, glycans, galactans, pectins, mannans, dextrins, polyacrylic acid, esters and amides and co-polymers thereof, polymethacrylic acid, esters and amides and co-polymers thereof, rubber latexes, poly(vinyl chloride) and copolymers, poly(vinyl esters) and co-polymers, poly(vinyl alcohol), polyamines, polyetyleneimine, polyethylene/polypropylene oxides, polyurethane, and aminoplast and phenoplast precondensates and polyamidoamine epichlorohydrin resins. The invention further concerns a process for its preparations, use thereof for the production of paper or non-woven, and a process for the production of paper or non-woven.