4. Assembly line workers build up rubber boots layer-by-layer, entirely by hand -- rubber boots are not made from molds, unlike the cheaper injection molded plastic boots. The form that the boot is built around is called a "last". Shoe lasts are usually made of low-cost polyurethane, but vulcanized rubber boots are placed in very hot autoclaves (vulcanizers), so a special aluminum alloy is necessary for rubber boot lasts.
Hand rolling is necessary to firmly bond successive layers of rubber and rubberized fabric together, since the contour of the last makes it difficult to mechanically press the layers together.
