Creosote or “soot” is caused by simply burning materials, such as wood, in your fireplace. There is no way to prevent the buildup of creosote. Now you are probably asking, “What is creosote?” It is basically unburned fuel that gathers in the form of black powder, flakes, or a baked-on glaze, depending on the degree of buildup. This is one of the main causes of chimney fires. When there is an excess buildup of creosote in the chimney and temperatures rise, the soot is ignited and an actual fire is started inside your chimney, showering your roof with sparks.