Among soft colloidal systems microgels, aqueous dispersions of nanometer or micrometer-seized hydrogel particles, have been the subject of intense research in the last years because of their versatility and high sensitivity to external stimuli. In particular the responsive hydrogel we are investigating is composed of Interpenetrated Polymer Network (IPN) of poly(N-isopropylacrylamide) (PNIPAM), a thermo-sensitive polymer, and polyacrylic acid (AAc), a pH-sensitive polymer, dispersed in water. The existence of a thermoreversible transition corresponding to the swollen-shrunken volume phase transition due to the presence of PNIPAM has been highlighted. Adding PAAc introduces an additional pH-sensitivity with respect to the temperature-sensitivity and leads to interesting differences in the transition process at acidic and neutral pH which need to be accurately investigated.