Made from seamless latex rubber, they are extremely strong, and by using a combination loops you can dramatically increase the resistance. The loop bands are circular and the size shown of 100cm (40") is when the rubber band is laid flat. The actual total length of the loop band (if cut and laid in a continuous length) would be 200cm (80"). Used in many fitness training programmes such as cross fit, weightlifting, stretching, plyometrics, rehabilitation, assisted pull ups.