The present invention relates to a method of manufacturing single and multi-core lifting slings, the method comprising: aligning a plurality of core fibers to form a sling body; applying a coating along length of the sling body, wherein an initial layer of the coating seals the plurality of core fibers from exposure to contaminates; and applying additional layers of the coating in areas of the sling body subject to high crush and shear forces. Other exemplary embodiments include tensioning the plurality of core fibers and forming a multi-core lifting sling by applying a seaming coat of the coating material to the sling body and at least to one of a second sling body. In an exemplary embodiment, the coating can be at least an isocyanate mixed with an amine forming polyurea.