Which icing type is best for creating smooth, rigid stripes on a cake?

Royal icing is the best choice for creating smooth, rigid stripes on a cake due to its properties and composition. This icing is primarily made from egg whites and powdered sugar, which allows it to dry to a hard finish. When piped onto a cake, royal icing retains its shape and provides a crisp, sturdy texture, making it ideal for decorating with intricate designs such as stripes.

Furthermore, royal icing can be manipulated to achieve various consistencies, enabling decorators to create both fine lines and thicker stripes with ease while maintaining a professional appearance. Its ability to set firmly means that the stripes will not smudge or lose their definition once applied to the cake.

Other icings, like buttercream, generally yield a softer finish that may not hold up well for detailed decoration. While fondant can also create smooth surfaces and can be rolled out into strips, it is not as easily manipulated for piping fine lines as royal icing. Star icing, typically used for decorative effects with a star piping tip, would not provide the necessary rigidity and smoothness required for crisp stripes. Therefore, the unique characteristics of royal icing make it the optimal choice for achieving the desired look on a cake.