VestPac H2OPac The lightest VestPac yet, the H2OPac weighs under 10 ounces! Our patented 3D Airmesh technology keeps you warm in the winter and cool in the summer while providing superior comfort and durability. Features a 6-way adjustable, rugged elastic "mono strap-front" for complete comfort Includes a 1 liter Zero-Taste reservoir with high flow 360 degree bite valve Can be worn as an "UnderPac" under a backpack to eliminate sweaty backs.