A plate fin heat exchanger is configured to receive hot flow from a hot source and cool flow from a cool source. The plate fin heat exchanger includes a plurality of plates arranged in parallel to define a plurality of flow passages there between, and a set of closure bars arranged at a first side of the plurality of plates to seal a first set of the flow passages against ingress of the hot flow, thereby directing the hot flow into a second set of the flow passages. Each respective closure bar includes an inner core formed of a first material having a first coefficient of thermal expansion and an outer cladding arranged about the inner core, the outer cladding formed of a second material having a second coefficient of thermal expansion. The first coefficient of thermal expansion is less than the second coefficient of thermal expansion.