High Sierra Explorer 55L Internal Frame Pack Aluminum frame 55-liter, top-load main compartment with gusseted drawstring closure and adjustable top lid. Front-load sleeping bag compartment with divider. ERGO-FIT shoulder harness, with adjustable load-lifters, is constructed with Vapel mesh Airflow and high-density foam padding. Molded foam back panel with Airflow&#8482 channels to keep your back cool and dry. Dual, contoured aluminum frame bars can be adjusted to fit the shape of your back.