A chimney cap is a protective covering installed at the top of a chimney flue, designed to shield the opening from environmental elements while allowing smoke and combustion gases to exit safely. Functioning as a primary defensive barrier, it prevents rain, snow, and sleet from entering the chimney, which helps avert water-related damage like masonry erosion and flue liner corrosion. Additionally, most caps feature mesh screening that acts as a spark arrestor to reduce fire risks and serves as a guard against debris and wildlife, such as birds and squirrels, from nesting inside and obstructing airflow. While primarily functional, chimney caps also offer an aesthetic finish to the chimney's silhouette, complementing the building's architectural style and improving overall energy efficiency by reducing downdrafts.