The gas transport parameters of 14 gases in poly[bis(trifluoroethoxy)phosphazene] were determined at temperatures ranging from about 12 to 45°C by the time-lag method. The phosphazene polymer demonstrated a high diffusivity; rather high crystallinity was expected, though. The permeation data determined were between polydimethylsiloxane and low-density polyethylene. The most interesting characteristic shown over the course of experimentation is that poly[bis(trifluoroethoxy)phosphazene] has significantly high solubility for CO2, as compared to other gases. The polar side groups—i.e., the electron-withdrawing trifluoroethoxy parts—which should contribute specific interaction with CO2, were shown to be stronger than their interaction with the polar N2O molecule. The sorption behavior is compared with those of other rubbery polymers, while phosphazene polymer characteristics are also discussed.