A hybrid membrane, also termed a mixed matrix membrane, consists of molecular sieving particles dispersed in a continuous polymer, so transport is governed by both phases ^[1]. The filler contributes a selective path whose pore size is fixed by its crystal structure, while the polymer supplies cohesion and processability, and the effective permeability then depends on filler loading, on particle-matrix contact and on interfacial voids or rigidified layers ^[1]. At low loading the particles stay isolated and transport follows a Maxwell-type average, whereas above the percolation threshold a connected filler network short-circuits the polymer and selectivity is set by the filler alone ^[2]. A predictive model therefore needs the intrinsic permeability of each phase and the adhesion across the boundary ^[2]. Functionalising the particle surface suppresses void formation and delays the loss of selectivity at high loading ^[3].