Salomon has ample experience on making running-specific packs, and this experience is very apparent in the Sense Pro 6 Set. The pack includes two 500 ml soft flasks, which flatten as they are deflated, preventing the formation of air pockets that would allow your drink to slosh around. The design process has included eliminating pressure points and potentially chafing structures. - Soft mesh material with effective moisture transfer - Two bottle pockets and extra pockets at front - Rear with main compartment - Tunnel-like pocket around the body - Adjustment at the front - Bottles are pvc-free, phtalate-free and bisphenol-free - Compatible with the separately available Custom Quiver (shown in one of the extra images) Choose size according to your chest circumference. If you're choosing between two sizes, the bigger one is the better choice. - 80-85 XXS - 85-91 XS - 91-97 S - 97-103 M - 103-109 L - 109-118 XL