The bottom of each glass has a 'rock', which creates a natural liquid motion - increasing the nosing of aromas. Fill the included silicone mould with water and put in the freezer to make a solid jumbo ice ball that outlasts traditional ice cubes. The shape of the glass makes rolling easy without spilling. A slight hand movement rolls the ice ball around the 'rock' evenly and cools your favourite scotch, whisky or spirit to perfection! Capacity 236 ml.