What characteristic of royal icing distinguishes it from flat icings?

The key characteristic that distinguishes royal icing from flat icings is its thicker consistency. Royal icing is made primarily from egg whites or meringue powder and powdered sugar, which gives it a firm texture that can hold its shape once dried. This thick consistency allows royal icing to be used for intricate decorations, such as piping detailed designs or creating stand-alone decorations like flowers and royal icing transfers. It dries to a hard finish, making it ideal for decorating cookies and cakes that require structural integrity and durability.

In contrast, flat icings typically have a thinner consistency, which makes them more suitable for glazing or adding a shine rather than for detailed decoration. While flavor, color options, and the presence of butter may vary between royal icing and other types of icing, the primary distinguishing feature remains the thickness and the way it sets, allowing for different applications in pastry artistry.