Stone Glacier's Sky 5900 is a heavy duty backpack designed for hardcore backcountry hunters and hikers. It features a generous 4300 cubic inch main compartment while in "bivy-mode", but this can be increased to 5900 cubic inches with the addition of a sky lid. Internal carrying capacity can be further increased by 2500+ cubic inches with the use of a load shelf, bringing the overall internal volume to an impressive 8000 cubic inches. Regardless of the configuration, virtually the entire contents of the Sky 5900 can be quickly accessed on the trail thanks to a 22" front vertical zipper, and attachment points for swing out pockets can be used to carry small items. The Sky 5900 is available with either a Krux frame or an Xcurve frame, with small, medium, and large belt options available for each. The Krux frame option was designed to be as lightweight as possible, whereas the Xcurve was designed with an emphasis on comfort and stability under the heaviest of loads. Just like all of Stone Glacier's frames, both the Krux and Xcurve feature an integrated Load-Shelf allowing the user to expand the bag off the frame to pack gear or meat in between the bag and the frame. This eliminates the need to put meat inside the bag and keeps the heaviest of loads more stable and closer to your back for increased comfort. Additionally, all past and current Stone Glacier bags and frames are interchangeable, allowing you to swap bags on and off your frame for different applications without needing to purchase and entirely new bag/frame system. Features of the Sky 5900 Backpack: Available with Krux frame or Xcurve frame 2 lbs. 4.2 oz. (bag only) 5 lbs. 1.4 oz. on Krux Frame w/ medium belt 5 lbs. 4.5 oz. on Xcurve Frame w/ medium belt 5,400 cubic inch main bag 4,300 cubic inch bivy-mode 96 L main bag with Sky Lid Hydration compatible Full panel zip for access to the main bag Front zipped pocket for quick access to essentials 150+ pound load rating Hydration compatible 2,500+ cubic inch expandable Load-Shelf Belt attachments Heavy-duty YKK #10 zipper Cordura 500 and Xpac fabric Heavy-duty, 1" Duraflex military approved buckles and webbing Made in the USA Stone Glacier Sky 5900 Pack w/Xcurve Frame Foliage 50075-FG