Install the included bracket to your saddle rails and snap the bag into place. Wrap the velcro of the front end around the seat post and after that all you need is to ride hard. The four-liter space is enough to hold more than a couple of inner tubes. The bag increases your visibility in the dark, as it's a relatively large, totally reflective object. Not suitable for use with carbon fiber seat rails or carbon fiber seat posts. - Waterproof material, welded seams - Splash-proof roller shutter - IP64 protection level: dustproof, resistant to spray from all directions - Front end velcro fastening fits max. 34.9 mm for the seat post - Lashing point for led light - Made in Germany - 5 year warranty The product does not contain PVC.