SIZE GUIDE: When measuring please measure around your waist where the belt will be placed. M = 26 to 34 inches. L = 32 to 40 inches. XL = 38 to 50 inches. The two firm elastic double-side pulls makes the belt fully adjustable, and there is also 2 plastic stays located at either end of the back panel to provide extra support. The breathable elastic side panels are great for letting your body breath making this belt perfect for comfortable prolonged use. The Neoprene back panel helps also helps to relieve lower back pain by using compression therapy and by trapping heat to give beneficial warmth. 20 health magnets are evenly positioned across the Neoprene back panel. The magnets will increase blood flow helping to relieve low back/lumbar pain.