Multiple layers of stiff paper (often red) rolled into a tight tube.
A "China Böller" is a simple but effective pyrotechnic device: China BГ¶ller Pyro Cracker
Modern regulations strictly limit the explosive content (often 50mg to 130mg depending on local laws) to ensure they are safe for consumer use while still being effective. History of Fireworks - American Pyrotechnics Association Multiple layers of stiff paper (often red) rolled
A gray "Chinese Fuse" is the classic ignition method, though modern variants may use more consistent visco fuses. China Böller Pyro Cracker