It meet size requirements for most airlines, enough room for 3 or 4 days trips. Comfortable day pack: breathable mesh shoulder straps with plentiful sponge padding help relieve the stress from your shoulder. Widened and thickened high elastic breathable back support for best ventilation and easing burden. Waterproof backpack: A rain cover included. The Rip-stop polyester material can prevent the water from sipping into the bag; if the heavy rain comes, then rain cover works Includes a few days limited for hiking backpack.