Abstract: Apparatus for initiating compressive treatment of a running length of flexible material wherein the material is confined against a moving drive surface by a confining surface and then retarded by a retarding surface located downstream of the confining surface and spaced from the drive surface. The material is pressed into driven engagement with the drive surface by pressing the confining surface against it while maintaining the retarding surface in ineffective position. The retarding surface is movable toward the drive surface to increase the retarding effect until satisfactory running condition is achieved. The thus pressed confining surface may be shifted upstream while the retarding surface is shifted to engage the material in the region vacated by the confining surface.