Nine different poly(n-isopropylacrylamide)based hydrogels, including nonionic, cationic, and anionic hydrogels, were synthesized in with and without the addition of pore-forming agents. The synthesized hydrogels were characterized with dry gel density measurements, scanning electron microscopy observations, and the determination of the swelling ratio swelling kinetics. All the results showed that the cationic hydrogels had faster swelling kinetics than the anionic and nonionic hydrogels. The addition of pore-forming agents (NaHCO3 and carboxymethylcellulose) during the synthesis process led to porous hydrogels with lower dry densities, swelling ratios, and swelling kinetic parameter values. An empirical equation was developed to successfully correlate the swelling kinetic parameter with the hydrogel swelling ratio. (C) 2004 Wiley Periodicals, Inc.