Thanks to its vest-like fit and carefully selected materials, the Traick 5 stays securely in place. A great choice for long training sessions and trail running use. The pack includes a built-in safety whistle, which is a mandatory item in some trail running events and a smart thing to carry anywayyou can blow a whistle much longer than you can shout. - Flexible chest strap structure - Elastic cord can be used as a compression strap or to hold running poles (see additional image) - Four easy-access pockets on each shoulder strap, including pockets suitable for soft flasks and zippered compartments - Zippered back pocket - Interior space fits a hydration bladder up to 2 liters (sold separately; Deuter's new Streamer II is a recommended option) - Reflective details - Key clip - The product contains no PFAS compounds and is Bluesign, Green Button, and ClimatePartner certified Choose your size based on chest circumference: - S: 89 cm95 cm - M: 96 cm102 cm - L