Woyo-shaper Xtreme Power Belt Fitness Waist Cincher Sport Shapewear Waist Sport Belt 4 Spiral steel bone, which is the fins material inside the corset. It's flexible and durable,can bend easily but recover quickly to origin. High elastic free support,helps with weight loss,reduces waist size,helps with posture Please refer to picture for detailed information and allow a little inaccuracy due to hand measure.