Due to size effects new challenges are involved in micro deep drawing compared to macro deep drawing. One of these challenges is that the limit drawing ratio in micro deep drawing becomes smaller than that in macro forming, which limits the application potential of micro deep drawing in an industrial context. In order to extend the application possibilities of micro deep drawing, investigations were carried out on this topic. Own previous work showed that the “tribological effect”, the “global flow behaviour effect” and the “local flow behaviour effect” are responsible for the lower forming limit in the micro range. In this paper, the flow behavior of thin foils is further investigated. Forming limit diagrams of Al99.5 and E-Cu foils with different thicknesses ranging from 20 μm to 100 μm were acquired using an optical measurement system. It was found that the forming limit of thin foils is lower than that of thicker foils. Further analysis indicates that this difference is due to the number of grains in the direction of thickness of the material: more grains give more grain boundaries, which allows more strain of the grains.