Cationic polymer thickener in particle form, said polymer consisting of a crosslinked water swellable cationic polymer comprising at least one cationic water soluble monomer and optionally at least one non-ionic water soluble monomer and/or at least one anionic water soluble monomer, wherein said polymer has a water extractable polymer content lower than 15 wt% as compared to the weight of the polymer, characterized in that said polymer is obtained by gel polymerization of said monomers in the presence of from 500 ppm to 10.000 ppm of crosslinking agent relative to the weight of the monomers wherein the water extractable polymer content is measured according to the following method: - step 1: polymer extraction - this step consists in separating insoluble polymer from water soluble polymer: 0.5 g (m0 in g) of polymer is added to a beaker containing 800 ml of deionized water, the resulting mixture is slightly stirred with a magnetic stirrer for 6 hours, then, 8 g of NaCl are added to complete the extraction, the resulting salt solution is still stirred for 1 hour, the polymer mixture is then filtered over a 100 μm screen, and 15 minutes later, the filtrate is then recovered in order to measure its weight (M0 in g), the polymer content "water extractables" in the filtrate is then titrated, - step 2: polymer titration by colloidal titration to determine charge density of cationic polymers as follows a potassium polyvinyl sulphate (PVSK) solution is prepared by dissolving in desionized water a PVSK polymer having a molecular weight of 243,300 g/mol, so as to obtain a solution having a concentration of 0.0025 N (N/400), a 0,1 N solution of chlorhydric acid is prepared in deionized water, titration is carried out on 30 g of polymer solution (filtrate) acidified with chlohydric acid (pH=4) and coloured with 2-3 droplets of blue indicator, the resulting PVSK solution is slowly added until the color turns from blue to violet, the water extractable polymer content is then determined according to (i) the volume of PVSK measured at equilibrium, (ii) the polymer composition, (iii) the polymer weight and (iv) the reagents molarity thanks to the following equation: % " Extractables " = Veq × N 400 × M 0 30 / m 0 × x y × 100 wherein: Veq: volume in ml of PVSK solution added at the equilibrium, N/400: concentration of PVSK in the PVSK solution (N=1), M0: mass in grams of the total filtrate recovered in step 1, "m0": mass in grams of polymer added in water in step 1, x corresponds to the percentage in weight of cationic monomers based on total amount of monomers, y corresponds to the molecular weight of the cationic monomer. - step 1: polymer extraction - this step consists in separating insoluble polymer from water soluble polymer: 0.5 g (m0 in g) of polymer is added to a beaker containing 800 ml of deionized water, the resulting mixture is slightly stirred with a magnetic stirrer for 6 hours, then, 8 g of NaCl are added to complete the extraction, the resulting salt solution is still stirred for 1 hour, the polymer mixture is then filtered over a 100 μm screen, and 15 minutes later, the filtrate is then recovered in order to measure its weight (M0 in g), the polymer content "water extractables" in the filtrate is then titrated, 0.5 g (m0 in g) of polymer is added to a beaker containing 800 ml of deionized water, the resulting mixture is slightly stirred with a magnetic stirrer for 6 hours, then, 8 g of NaCl are added to complete the extraction, the resulting salt solution is still stirred for 1 hour, the polymer mixture is then filtered over a 100 μm screen, and 15 minutes later, the filtrate is then recovered in order to measure its weight (M0 in g), the polymer content "water extractables" in the filtrate is then titrated, - step 2: polymer titration by colloidal titration to determine charge density of cationic polymers as follows a potassium polyvinyl sulphate (PVSK) solution is prepared by dissolving in desionized water a PVSK polymer having a molecular weight of 243,300 g/mol, so as to obtain a solution having a concentration of 0.0025 N (N/400), a 0,1 N solution of chlorhydric acid is prepared in deionized water, titration is carried out on 30 g of polymer solution (filtrate) acidified with chlohydric acid (pH=4) and coloured with 2-3 droplets of blue indicator, the resulting PVSK solution is slowly added until the color turns from blue to violet, the water extractable polymer content is then determined according to (i) the volume of PVSK measured at equilibrium, (ii) the polymer composition, (iii) the polymer weight and (iv) the reagents molarity thanks to the following equation: % " Extractables " = Veq × N 400 × M 0 30 / m 0 × x y × 100 wherein: Veq: volume in ml of PVSK solution added at the equilibrium, N/400: concentration of PVSK in the PVSK solution (N=1), M0: mass in grams of the total filtrate recovered in step 1, "m0": mass in grams of polymer added in water in step 1, x corresponds to the percentage in weight of cationic monomers based on total amount of monomers, y corresponds to the molecular weight of the cationic monomer. Veq: volume in ml of PVSK solution added at the equilibrium, N/400: concentration of PVSK in the PVSK solution (N=1), M0: mass in grams of the total filtrate recovered in step 1, "m0": mass in grams of polymer added in water in step 1, x corresponds to the percentage in weight of cationic monomers based on total amount of monomers, y corresponds to the molecular weight of the cationic monomer.