ABSTRACT Thermodynamic and kinetic aspects of CO 2 sorption and the resulting swelling are investigated in several commercial polymer‐based medical devices and packaging materials, using in situ FTIR spectroscopy under mild processing conditions (40°C–50°C and 8–20 MPa). At thermodynamic equilibrium, significant CO 2 uptake (up to 41% w/w) and volume swelling (up to 62%) are observed in silicones and poly(L‐lactide‐co‐ε‐caprolactone) copolymers, whereas limited sorption occurs in polyolefins (polypropylene, high‐density polyethylene) and in polyester films coated with low‐density polyethylene. These differences are attributed to intrinsic polymer properties; sorption and swelling are favored in polymers combining a highly amorphous structure with elevated chain mobility, and the presence of functional groups with chemical affinity for CO 2 . Among the studied materials, glycol‐modified polyethylene terephthalate exhibits a distinct behavior, characterized by initial CO 2 uptake followed by pressure‐induced crystallization after several hours of exposure.