Fluoropolymer flexible element material for fabric expansion joints are generally reinforced with fiberglass, and have a PTFE laminate layer of variable thicknesses between 4 and 30 mils. They have excellent chemical resistance, zero porosity, and can be used in wet or dry service. But they should be protected from abrasive media with a baffle (liner). Rated for 600F.
Other reinforcing materials are available, including aramid, polyester, and others.
See below for typical movements for a given face-to-face width.
Some typical configurations are shown below.