Designed to embody of spirit of a runner this race vest has room for your extra, gear, hydration, and more. We considered every detail, edge, and stitch. Like a second skin you'll forget it's there until you need it. Contoured to fit the female figure this vest is the pinnacle of race vests on the market. This vest is ideal for those users looking for an apparel like fit. The new edition of this snug-fitting, body-mapped hydration pack developed in collaboration with elite endurance runner Stephanie Howe now features an Insulated Bladder, for colder water over the long-haul. This vest has virtually no bounce and room to carry your gear, nutrition, or additional water. Run longer. Run stronger. SIZING - The sizing is based on a chest circumference measurement taken around the sternum and will be as follows: XXS 28-30.5 (71-74cm), XS 31-32.5 (76-79cm), S 33-34.5 (81-84cm), M 35-36.5 (86-89cm), L 37-38.5 (91-94cm) L 37-38.5 (91-94cm) XL 39-40.5 (96-99cm)