Two batches of poly(vinylidene fluoride hexafluoropropylene) [P(VDF-HFP)] copolymer with different monomer ratios were thoroughly characterised and cast into membranes to relate the fundamental properties of this copolymer with its performance in CO2 separation. Solubility testing revealed that the PVDF part of the copolymer was dominating and calculations with Hansen's solubility parameters corroborated the outcome. A very slow solvent evaporation rate and use of solvents with a high boiling point were found to be essential in the formation of defect-free membranes from this copolymer for gas separations. Physical examination, DSC, XRD and TGA were also performed to better link the fundamental membrane properties to the gas separation performance. A low crystallinity in the prepared P(VDF-HFP) membranes was favourable in terms of compatibility, solubility, membrane formation and CO2 separations. (C) 2014 Elsevier B.V. All rights reserved.