For that, a binder is needed to physically hold the chemicals together. A number of chemicals can be used for this purpose, but the most common is dextrin. Dextrin is actually a name for a group of smaller carbohydrates produced by the breakdown of starch; it can also act as a fuel, though in the amounts used in sparklers it doesn’t really contribute a great deal to the pyrotechnics. Water is also required in order to form a paste, though obviously the sparklers must consequently be dried before they can be burned.