It is a cord with a black powder core. There are three layers to visco fuse. First one layer of string is wound around the core, then a second, less tight layer of string is wound in the opposite direction to prevent unraveling. The last layer is a low-nitrate nitrocellulose lacquer. The last layer is to water-proof the strand and to prevent it from falling apart.
Cannon Fuse is a visco fuse that is most often thicker, steadier burning, and is coated to be more water-proof. Most cannon fuses of high quality can burn while under water. Cannon fuse is normally green or red in color. When using anything with a fuse, remember that it can't be put out.

Flying fish fuse is a modified type of Visco-type fuse used in fireworks. The composition in the core is a metallic spark composition or other effect instead of/as well as black powder. Flying fish can thus perform as a main effect instead of just an initiator. For example, simply lighting a short piece of flying fish on the ground makes it fly through the air, seeming to swim in random directions, while emitting sparks and noise. A aerial shell loaded with many such pieces results in a beautiful myriad of pieces flying and sparking high in the air.65 feet of Blue Visco Quick fuse 2.5 mm burns hot enough to easily ignite other fuses for your grand finale as you can chain multiple products together. Burns at Quick rate of 4 seconds per foot.