This paper proposes two applications of quantitative tomography. Assuming that the attenuation ratio of the x-ray beam throughout the investigated sample can be evaluated with high accuracy, this paper deals with quantitative characterization of glass wool structure. In a first part, we measure the 3D spatial distribution of density in a sample that has been extracted from a glass wool plate. The calibration is performed and an experimental validation of the technique is realized. The heterogeneity of the material is characterized and explained in relation to manufacturing methods. In a second step, we follow the evolution of this distribution during a mechanical test. For this purpose, an original device has been developed in the laboratory in order to perform a tomographic process during a mechanical load. The proposed method compares the density distribution between two different compression steps and determines the evolution of density inside the sample. The local strain is evaluated along the stress direction. These first results allow assumptions about the relationships between structure and properties to be expressed.