VestPac’s are lighter and more comfortable than any hydration pack on the market. They are so slim, you can where them under your outer clothing layers! The revolutionary 3-D Airmesh adapts to any climate, keeping you cool in the summer and warm in the winter. Convenient chest pockets provide ample storage for your valuable electronics and accessories. The low-profile back panel houses a hands-free hydration system. The form-fitting, athletic design guarantees maximum comfort, durability, and style; while heavy duty elastic straps ensure a perfect fit for all sizes.