AbstractThe solubility of CO2 in PETG, a glycol‐modified PET, was measured at different temperatures and over a broad pressure range, and diffusion coefficients were derived at the corresponding conditions. The solubility of CO2 is quits high. For example, almost 15 wt% CO2 can be dissolved in PETG at 35°C and 6.0 MPa. Consequently, CO2 is good blowing agent for PETG. Cellular foams in the density range of about 0.04 to 1.2 g/cm3 and diameters in the range of about 10 to 150 µm were produced. The foam density and the cell size were found to depend on the foaming temperature and time, with larger cells obtained at higher temperatures or when the sample was foamed for a longer time. The foam density decreased with an increase in the foaming temperature to about 90°C, beyond which the density tended to increase slightly due to the cell collapse or coalescence. The density reduction also depended on the pressure at which the polymer was saturated with CO2; the higher the saturating pressure at a given temperature, the greater the density reduction.