While the neat PSU offers a permeability of P(He) = 9.13 Barrer and P(CH 4 ) = 0.16 Barrer with a selectivity α(He/CH 4 ) = 57, following an almost linear trend the 20wt.% MIL-116(Ga) MMM offers a permeability P(He) = 37.40 Barrer and P(CH 4 ) = 0.03 Barrer and a selectivity of α(He/CH 4 ) = 1190. It must be stressed that these values have been generated for a feed mixture of 4:96 He to CH 4 , offering a huge increase in performance when considering the differences in chemical potential to a 50:50 mixture.