Fluoroelastomer (FKM) is a high performance elastomer flexible element material for fabric expansion joints, and are usually reinforced with fiberglass.  They have outstanding resistance to chemicals, oils, and heat compared with other elastomers. Also an advantage is their excellent abrasion resistance that generally may not required protection from the media.  Normally rated for 400F.  (Note that Flexicraft also provides fully molded duct expansion joints in these materials.)

Avaialble in 1/8" and 1/4" thicknesses. 

Movements for Fluoroelastomer Fabric Expansion Joints

See below for typical movements for a given face-to-face width. 

Movements for Fluoroelasomer Fabric Expansion Joints

Some typical configurations are shown here. 

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