The Ocean Band is made from a high-performance elastomer in a tubular structure. This allows you to stretch it for a perfect fit, even over a wetsuit. The titanium buckle and adjustable loop secure the band during high-speed water sports. To wear the Ocean Band over your thickest wetsuit, a separately sold extension is available. The Trail Loop, Alpine Loop, and Ocean Band were designed for the Apple Watch Ultra and fit perfectly with the 49 mm case. The bands are also compatible with the 44 mm and 45 mm cases.