LARGE OPENING FOR EASY CLEANING & FILLING – Our hydration bladder has one of the largest opening on the market. The big opening makes for easy pouring of water. It is also fairly wide for a hand or bottle brush easily access to the interior hydration bladder. The 4” screw on cap goes on and off easily. For cold water, simply add ice cubes directly from a scoop or refrigerator ice dispenser. The smooth inner of water reservoir promotes health and is easy to clean.