6X powdered sugar is describing the particle size of the sugar. 6X sugar is primarily used for making icing. It is finer than the sugar you buy in the grocery store but not as fine as 10x. 10x sugar contains more cornstarch to help the sugar from sticking to itself. Thus some would say that your icing would be less sweet with the 10x due to more cornstarch. The higher the number, the finer the grind of powdered sugar.

A number of desserts and sweets are not complete without a final dusting of confectioner’s sugar, also known as powdered sugar or icing sugar. Confectioners sugar is actually granulated sugar which has been mechanically ground into a very fine powder. This powdered form of sugar is commonly used to make cake frostings, sugar glazes, dessert sauces and decorative icings. Confectioner’s sugar is also used to provide additional sweetness to fried donuts, funnel cakes and beignets.

Confectioners sugar is rarely used as a substitute for regular granulated sugar in recipes for a number of reasons. The ratio of confectioner’s sugar to granulated sugar would make most recipes cost-prohibitive, for one thing. Confectioners sugar also does not tolerate long periods of heat, which makes it much more suitable for cold icings and glazes, not heated sauces or custards. Confectioners sugar also contains up to 3% cornstarch as an anti-caking agent.