However, the WVTR of the PEFA films was measured to be 2660 ± 73 g μm day -1 m -2 (50 -0 % RH), higher than that reported for PLA and close to PCL in similar conditions. Thus, despite the cross-linked nature of the polyester produced in this study and the long starting monomers (C18), the presence of unreacted hydrophilic functionalities undermines to some extent its water barrier properties resulting in WVTR comparable to PCL but far from PE. A similar conclusion was drawn for a cross-linked polyester film obtained from aleuritic acid (9,10,16-trihydroxy hexadecanoic acid), where the residual polar functionalities led to values of WVTR 40 times higher than what was measured for PLA or PCL. This analysis is also coherent with the increase in WVTR measured following the "water method" (when the imposed gradient across the film is 100 -50 % RH). In such conditions, the plasticizing effect of water is more relevant, with the WVTR for the PEFA film approximately doubled, reaching 5463 ± 328 g μm day -1 m -2 . Visual observation confirms such a hypothesis, with the film swelling during the water method. However, at lower RH the film has a limited moisture uptake (𝑤𝑤𝑡𝑡 𝐻𝐻 2 𝑂𝑂-50𝑅𝑅𝐻𝐻% = 0.6 ± 0.2 %). The PEFA film WVTR remain promising, being considerably lower than other bio-based materials such as chitosan and thermoplastic starch.