A cartridge (12) for a viscous-material dispenser includes a plunger (10) that is slidable within a cylinder (18). A seal body (104) forms between an outer circumferential surface (82) of the plunger and an inner circumferential surface (84) of the cylinder when a viscous material flows into a radial tubular clearance (106) that continuously extends both axially and circumferentially between the outer circumferential surface and the inner circumferential surface. Ridges (100) may be formed on the outer circumferential surface of the plunger to guide the inflowing viscous material and facilitate the formation of the seal body.