Abstract A unique experimental method for analysing mass transfer between gaseous flows has been presented. It consists of the measurement of Lagrangian quantities, linked to intermaterial surfaces evolution generated by means of a pulsed smoke wire technique. Stretch intensity, stretch rate, mixing-layer thickness, separation distance between neighbouring segments of the interface, for a purposely designed prototypical quasi-two-dimensional flow configuration, have been measured against time and presented in terms of their statistical distribution and averages. A peculiar regime named ‘isolated mixing-layer regime’ has been identified by means of comparison of the mixing-layer thickness with the interface separation distance. Further, the direct experimental evaluation of the stretch rate of the intermaterial surface allows the evaluation of the role of the kinematics on reactive mixing-layers, in particular in the case of the stretched diffusion flame.