Properties of four polymers of intrinsic microporosity containing Trager's base units were assessed for CO2 capture experimentally and computationally. Structural properties included average pore size, pore size distribution, surface area, and accessible pore volume, whereas thermodynamic properties focused on density, CO2 sorption isotherms, and enthalpies of adsorption. It was found that the shape of the contortion site plays a more important role than the polymer density when assessing the capacity of the material, and that the presence of a Trager base unit only slightly affects the amount adsorbed at low pressures, but it does not have any significant influence on the enthalpy of adsorption fingerprint. A comparison of the materials studied with those reported in the literature allowed us to propose a set of guidelines for the design of polymers for CO2 capture applications.