Description BlackJack Tire Repair uses twelve strands of high-tensile Kevlar fiber, the same materials used in bullet-proof vests. Many competitors use as few as seven strands. Each strand of fiber is individually impregnated with live butyl rubber. This compound is developed using carbon black, giving the repair its black color, making the repair almost invisible. BlackJack conforms to the size and shape of the injury, sealing out moisture and dirt, eliminating stress to the belts and preserving the tire body.