Epitaxial foils grown on re-usable porous substrates have the potential to streamline the germanium wafer value chain and thus limit the usage of this critical raw material. The suitability of this approach for producing high efficiency multijunction solar cells has recently been demonstrated. This contribution aims at giving an overview of the concept and its recent advances. It also demonstrates wafer re-use with a second-generation foil of 19-cm diameter, and reports carrier mobilities for doped foils, grown at 70 and up to 185 nm/min with GeCl₄.