an exercise and / or play hoop , made of semi - rigid plastic tubing , is partially filed with water to between ⅙ and ½ full , most preferably ¼ full . the water improves the dynamics of the hoop and makes it easier to keep the hoop elevated by gyration . the hoop is made of a length of hoop tube bent into a circle . a coupling tube is inserted where the ends abut , spanning the joint . the coupling tube includes a bore through which the liquid flows circumferentially around inside the hoop , and past the joint . the joint is sealed on the outside with a shrink - plastic tube . a decorative , preferably iridescent cover may cover the hoop .