EPDM elastomer flexible element material for fabric expansion joints are reinforced with fiberglass, are available in 1/8" and 1/4" thicknesses, and are normally rated for 300F. Low cost, with high tensile strength and excellent resistance to oxygen and ozone. They also have good flexing characteristics.
Other available elastomers are neoprene (250F), chlorobutyl (250F), and silicone (450F). If needed, the reinforcement can also be changed to aramid blend, polyester, and others. The thickness can also be changed. (Note that Flexicraft also provides fully molded duct expansion joints in these materials.)
See below for typical movements for a given face-to-face width.
Some typical configurations are shown.