A hydration pack is a type of backpack designed to hold water and allow for easy drinking while on the move. It typically features a built-in water reservoir, often made of flexible plastic, and a tube that extends to the front for convenient sipping. Hydration packs are popular among outdoor enthusiasts, such as hikers, cyclists, and runners, as they provide hands-free hydration. These packs come in various sizes and styles, catering to different activities and preferences. Some may include additional compartments for storing gear, snacks, or personal items. Brands like CamelBak and Osprey are well-known for their quality hydration packs, making them a favorite choice for adventurers.