Store your sugar in a tightly sealed container, as it is prone to clumping.
Icing sugar in Britain is the name of white granulated sugar that is ground and sieved to a smooth powder, in terms of size it is finer than caster sugar and has a fine silky texture. When intended for home use, it typically contains a small amount of anti-caking agent.
It is called icing sugar as it is typically used to make icing.
Because of its super fineness, when used in baking, it is ideal for icings and butter creams as it combines easily and dissolves instantly without the need for heat.
Icing sugar can be prepared at home by grinding 1 cup of granulated sugar with 1 tablespoon of cornstarch for several minutes in a food processor or coffee grinder till a powder forms. Please be aware that if you make your own icing sugar in your food processor it will more than likely scratch up the plastic bowl.