Porous trailing edges attenuate hydrodynamic pressure fluctuations that scatter as trailing-edge noise, with their effectiveness governed by their material parameters. Conventional measurements of permeability rely on steady-flow rigs, which cannot capture the dynamic response of this parameter, which is relevant for predicting balancing pressure fluctuations under grazing-flow conditions. In this study, we introduce a method for directly determining the dynamic permeability of porous trailing edges from time-resolved particle image velocimetry (PIV) data. The approach employs a lumped-system circuit analogy that links unsteady pressure gradients to through-material velocities, enabling in situ characterisation without specialised porous rigs, thereby further extending its applicability to thin trailing-edge geometries. Two materials with similar porosity but distinct internal architectures are compared against a solid baseline: a structured porous trailing edge (SPTE) and a random foam trailing edge (RFTE). The extracted permeability curves show close agreement with the analytical model of Johnson et al. (J. Fluid Mech., 1987, vol. 176, pp. 379–402), validating the method for both structured and randomised porous materials. The procedure also allows for the estimation of the equivalent viscous characteristic length and tortuosity. A detailed comparison reveals that the SPTE exhibits a lower viscous length scale and tortuosity than the RFTE, with a relatively higher dynamic permeability response at high frequencies.