Baked products with various expanded structures were obtained by changes in process conditions and formulation. A device was set up to measure their gas permeability coefficient, k (from 10⁻¹² to 3.6.10⁻¹⁰ m²) and then relate it to their structural features. The device consists of an hermetic cell connected to gas flow rate sensor and allows for modification of the sample density through compression. For a laminar air flow, k is determined by the measurement of the differential pressure, according to Darcy's law. Gas permeability on uncompressed and in situ compressed crumbs, with apparent density ρ* varying from 0.20 to 0.50 g/cm³, were found to depend on their porosity ε following the Carman-Kozeny's model. However, the deviation from theoretical values can not be explained by a simple model based on the tortuosity. Results highlighted the role of the expanded structure, mainly pore size and shape. This device may be used to measure these important properties that influence mass transfer in aerated foods and complement the characterization of their structure.