SUNVP 12L School Backpack Daypack for Cycling Hiking Hunting Camping Trekking Day Travel Material:Water-Resistant,Anti-friction Nylon Size:17.32(H)*5.9(L)*9.45(W)Inches.Suitable for short distance travel or go out. Set-up for a hydration system.Thermal insulation layer on the side part to keep the water warm no matter in Spring,Summer,Autumn and Winter. Back within porous honeycomb design,high elastic on both sides by three-dimensional combined closely with the breathable sponge with breathable mesh yarn, white gauze by phase between fixed, back in the middle is hollow out state, thus good solve the ventilation resistance, effectively keep the contact parts of the body heat sweat, comfortable effect Reflective bar on the bag to be more visiable in the dark. Making you more safey.