A flexible substrate are disclosed comprising an amorphous inorganic composition, wherein the substrate has a thickness of less than about 250 μm and has at least one of: a) a brittleness ratio less than about 9.5 (μm)−1/2, or b) a fracture toughness of at least about 0.75 MPa·(m)1/2. Electronic devices comprising such flexible devices are also disclosed. Also disclosed is a method for making a flexible substrate comprising selecting an amorphous inorganic material capable of forming a substrate having a thickness of less than about 250 μm and having at least one of: a) a brittleness ratio of less than about 9.5 (μm)−1/2, or b) a fracture toughness of at least about 0.75 MPa·(m)1/2; and then forming a substrate from the selected inorganic material.