A criticism is offered in this paper of conclusions stated in two recent works [Marand and Surapathi, J. Membr. Sci. 415 (2012) 871; Singh et al., J. Membr. Sci. 448 (2013) 160] with reference to properties of composite materials which are relevant to the determination of steady state permeance of solute species. The discussion aims at clarifying conditions for the validity of "permeability models", which claim for the role of the permeability ratio P-A/P-B in a binary composite of phases A and B, as the only parameter needed to estimate the overall relative effective permeability P-M/P-B, when size/shape distribution and arrangement of domains of the two phases are assigned. In this note, the thesis is rejected of a separate role for the solubility or partition coefficient in the performance of mixed matrix membranes and attention is driven to published numerical results which deserve to be revised. (C) 2014 Elsevier B.V. All rights reserved