A stator vane for a gas turbine engine comprising: a platform; an airfoil extending from the platform, the airfoil having a core configured to transmit coolant and extending from the platform into the airfoil, the core having an axial inner wall and an outer sidewall defining a portion of the airfoil and having a sidewall perforation therethrough configured to allow a flow of coolant from the core through the airfoil; and a thermally driven spring valve comprising: a metallic sheet comprising a base, an exterior surface, and an interior surface, characterised in that the sheet has cutouts forming a first finger portion extending from the base and a second finger portion extending from the base, the exterior surface extending from the base over the first finger portion and the second finger portion and the interior surface extending from the base over the first finger portion and the second finger portion; wherein the first and second finger portions (304, 306) are curled to have a first curvature vector and a second curvature vector, respectively; wherein the first finger portion is curled such that the exterior surface of the first finger portion is disposed proximate the interior surface extending from the base, and wherein the second finger portion is curled such that the exterior surface of the second finger portion is disposed proximate the interior surface extending from the base; wherein the thermally driven spring valve is disposed within the core and coupled to a core wall at the base; and wherein the first finger portion and the second finger portion of the thermally driven spring valve are configured to restrict the flow of coolant through the sidewall perforation by the exterior surface of the first and second finger portions (310, 312) selectably obstructing the sidewall perforation in response to thermal expansion of the metallic sheet. a platform; an airfoil extending from the platform, the airfoil having a core configured to transmit coolant and extending from the platform into the airfoil, the core having an axial inner wall and an outer sidewall defining a portion of the airfoil and having a sidewall perforation therethrough configured to allow a flow of coolant from the core through the airfoil; and a thermally driven spring valve comprising: a metallic sheet comprising a base, an exterior surface, and an interior surface, characterised in that the sheet has cutouts forming a first finger portion extending from the base and a second finger portion extending from the base, the exterior surface extending from the base over the first finger portion and the second finger portion and the interior surface extending from the base over the first finger portion and the second finger portion; wherein the first and second finger portions (304, 306) are curled to have a first curvature vector and a second curvature vector, respectively; wherein the first finger portion is curled such that the exterior surface of the first finger portion is disposed proximate the interior surface extending from the base, and wherein the second finger portion is curled such that the exterior surface of the second finger portion is disposed proximate the interior surface extending from the base; a metallic sheet comprising a base, an exterior surface, and an interior surface, characterised in that the sheet has cutouts forming a first finger portion extending from the base and a second finger portion extending from the base, the exterior surface extending from the base over the first finger portion and the second finger portion and the interior surface extending from the base over the first finger portion and the second finger portion; wherein the first and second finger portions (304, 306) are curled to have a first curvature vector and a second curvature vector, respectively; wherein the first finger portion is curled such that the exterior surface of the first finger portion is disposed proximate the interior surface extending from the base, and wherein the second finger portion is curled such that the exterior surface of the second finger portion is disposed proximate the interior surface extending from the base; wherein the thermally driven spring valve is disposed within the core and coupled to a core wall at the base; and wherein the first finger portion and the second finger portion of the thermally driven spring valve are configured to restrict the flow of coolant through the sidewall perforation by the exterior surface of the first and second finger portions (310, 312) selectably obstructing the sidewall perforation in response to thermal expansion of the metallic sheet.