This great looking lightweight black bracelet with our Sine Wave Logo in Blue is made of pure silicone. Imprinted at our original Frequency (7.83Hz Schumann Resonance). Available in five sizes: Extra small is 6.25 inches, great for children or women with smaller wrists. Small is 6.75 inches and is perfect for larger children and most women. Our medium is a good fit for most women and some men with a length of 7.5 inches. Large is 8 inches and will fit the majority of men. Our extra-large is 8.5 inches and is a good fit for the bigger wrist or small ankle.