An improved heat exchanger that reduces the thermal stress in components thereof especially tube plates or tube sheets so as to enable greater temperature differences across adjacent components while reducing the temperature gradient and thus extending the life of the heat exchanger is accomplished by attaching or bonding an insulating material of low thermal conductivity such as a sheet of PTFE, a metal jacketed layer of insulating cork or nonmetallic composite such as micarta sheeting to the metal component or tube sheet or tube plate.