Fishpond Thunderhead Submersible Lumbar The Thunderhead Lumbar is a fully waterproof pack that is built with your comfort and personal gear in mind, even when you find yourself in the worst conditions. Updated for 2022 - features the True Zip self healing fully submiersible zipper Go ahead, wade deep or wade out in saltwater - this pack will keep your gear safe and dry 13.5" x 9" x 5" -10L or 610 cu. in.