Abstract: A motion bead filler strip for application to the spaced flanged edges of expanded steel lath used in plaster finished walls flexibly seals expansion joints in such walls. The filler strip is an elongated cross sectionally inverted V-shaped outwardly flanged member formed of a flexible synthetic resin, the flanges being inturned toward the V-shape and provided with longitudinally extending ribs on their outermost surfaces. The inturned portions of the flanges define continuous pockets registrable over inturned flanges on the longitudinal edges of conventional expanded steel lath.