Constructed of high-quality, professional-grade materials and won't pop if punctured. Instead, they deflate slowly, significantly reducing the risk of injuries if a puncture occurs while in use. Easy to inflate, and includes a tape measure that makes it easy to tell when you've added the right amount of air. Sold individually. Storage options and pumps available; Features: Promote proper posture, increase lower back mobility, build back and abdominal strength. Improve core strength. High quality professional grade PVC construction. Available in 4 sizes and 5 colors. Tape measure included to indicate proper inflation User's Height Listing: 45 cm: 4'6" to 5'. 55 cm: 5'1" to 5'7". 65 cm: 5'8" to 6'1". 75 cm: 6'2" to 6'7".