A flexible substrate for a TFT includes a metal substrate having a predetermined coefficient of thermal expansion, and a buffer layer on the metal substrate, the buffer layer including a silicon oxide or a silicon nitride, wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows, α f + 0.162 × ( 1 - v f ) E f ≤ α s ≤ α f + 0.889 × ( 1 - v f ) E f Ef representing Young's modulus of the buffer layer, vf representing Poisson's ratio of the buffer layer, αf representing a coefficient of thermal expansion of the buffer layer, and αs representing the predetermined coefficient of thermal expansion of the metal substrate.