The best material to practice piping would be buttercream icing or royal icing. Both of these icings have the appropriate consistency for piping and allow you to create various intricate designs on your cakes or cupcakes. Buttercream icing is softer and more forgiving, making it an excellent choice for beginners as it allows for mistakes to be easily corrected. Royal icing, on the other hand, dries firm and holds its shape well, making it ideal for more advanced piping techniques such as intricate lacework or delicate details.