Root phenotypes are of great interest for understanding and optimizing the interaction of plants with their biotic and abiotic environment. Physiological media (e.g., soil) is opaque, which complicates the phenotyping of roots in vivo. Hydroponic conditions are transparent but lead to non-physiological root development. To address this issue “transparent soil (TS)” was created, which combines the structural heterogeneity and aeration of soil with the transparency of hydroponics to yield root phenotypes in vivo for breeding and research. The material is transparent in MS media or soil extract, which enables the phenotyping of root systems in vivo during the growth of the plant both in macroscopy and microscopy. The granularity of the soil can be changed to affect the effective porosity of the TS, ranging between that of sand and that of loam. This poster will show the optical and mechanical characterization of the TS, as well as evidence of its effect on root phenotypes on model plants such as Glycine max, Brassica rapa and Arabidopsis thaliana. It will also show the possible applications of TS in varied research interests, e.g., studying root tropisms responses to nutrient, water availability, and mechanical heterogeneities of the media.