The toughest part about figuring out caster sugar is that it has several different names. Caster sugar is also known as castor sugar, superfine sugar, or even bakers sugar. This is not to be confused with another sugar you may have used, which also has a few different names: powdered sugar, also known as icing sugar or confectioners sugar. Powdered sugar is ground into such a fine grain that you can barely see the individual grains with the naked eye. Superfine or caster sugar, on the other hand, is still granular sugar, just a smaller grain than your typical sugar. Think of caster sugar as the medium point between your normal sugar and your powdered sugar.