Description 600D Polyester and Diamond Ripstop with a water resistant coating,Features a 4-Point air mesh backing system, side compression straps,Built-in safety whistle integrated in the buckle and adjustable shoulder/sternum straps for a precise fit,Long U-shaped zippered opening makes it easy to get inside,Two front zippered pockets, a secondary compartment with organizer and elasticized inside pocket,side mesh pockets, gear attachments and D-rings and a top handle,Includes reflective accents on the back, front and side of the bag so you can be seen at night,Note this bag is (H20) 2L hydration compatible