The inventive deckle piston compression and adjustment mechanism is used in changing the coating width of a die manifold. The deckle consists of elongate positioning shaft for positioning the deckle in the die manifold. A deformable sealing piston formed of Rulon LR is carried by the shaft and is constructed and arranged to substantially fill the die manifold. An expansion mechanism is used to expand the Rulon seal, thereby causing the deformable seal to expand to form a seal in the die manifold.