polyester COMPACT& LIGHTWEIGHT : This Hydration packs are designed specifically for road cycling /running/ Hiking ,So that's Compact and low-profile so they feel light and stable on your back and wont create a ton of wind resistance ,keep your body functioning at peak performance whether you're training for a marathon or cycling.INSULATED WATER BACKPACK: Hydration pack have thick insulated layer ,the insulated bladder compartment to keep water cold for hours. PROFESSIONAL 2L HYDRATION BLADDER:The 2L liner inside detaches from the backpack for easy cleaning and assembly. The rubber mouthpiece has a simple switch valve to stop water flow when needed, ensuring a leak free outdoor experience. Our water liners have passed pressure tolerated tests and have been put to the test to highest quality standards. COMFORTABLE & RELIABLE:Adjustable straps help tailor the hydration pack to your needs. For bikers, the hydration fits perfectly between most shoulder blades, as to not catch on anything while biking or even hiking. The design is not a traditional hydration pack because it centers the weight on to your back rather than your shoulders, as more traditional hydration packs do. VERSATILITY :Internally the hydration pack contains a separate pocket for other items, such as a phone, first aid kit, and snacks.The hydration pack is your perfect choice for cycling, camping, running,music festival, rave , kayaking. A decent Holiday Gift for families and friends who love outdoor sports.