Black Jack Large Diameter Refills (Box of 50) BlackJack's Tire Repairs are manufactured using 12-Strands of High-Tensile Kevlar fibers, the same materials used in bullet-proof vests. Many competitors use cotton or polyester fiber strands. Each BlackJack 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 in the tire. Carbon black also increases the strength and wear resistance of rubber.