"X30" signifies that this necklace is permeated with Aqua-Titanium X30, which is 30 times more concentrated than standard Phiten necklaces. Stronger effect for hard-core athletes. The strands of this revolutionary necklace are coated with Aqua-Titanium. Its core has micro-sized titanium spheres, as well as carbonized titanium. It can also be worn on the wrist, ankle or waist to quickly relieve pain and stress. Recommended for sports lovers, enhancement of athletic abilities, fatigue reduction, relaxation and refreshment.