Sinew is the tendons and ligaments of animals. Plains Indians used sinew from the buffalo like we use thread, rope, or glue. Modern sinew thread is artificially made from synthetic fibres to reproduce the effect. Heavy, waxed polyester fibres are spun into a strong and realistic imitation of natural sinew. This artificial sinew is great for stitching leather, using on beading projects and weaving dream catchers.. It can be split down in just the way original sinew could be.