These ice ball trays are made of hard plastic which makes the round ice cubes easier to release than a silicone mould. After taking the mould out of the freezer, slightly twist the tray to release the ice. Simple to use, just pour approx 300ml of liquid into the tray at one time and put the ice cube mould into the freezer for approx 4 hours, you can get 33 sphere ice balls ready. Comes with a unique design which will fit into your circular glass with ease, you won't need to smash the ice up for it to fit in a glass.