The Proviz Switch Backpack coveris adjustable and designed to fit over all standard size rucksacks (up to 35L capacity). The Proviz Switch Backpack cover is made from a dual-layer waterproof outer shell that can be used either way to give the user two options, one for the day and one for night. By day, the lightweight fluorescent yellow waterproof material helps to keep you clearly seen on the roads. At night you Switch it around so the reflective material lights up when vehicle headlights are shined upon it enabling the user to be seen more clearly on the roads, therefore allowing drivers to adapt accordingly to your position on the road. The backpack cover is 100% waterproof and is attached using two elastic straps across the back of almost any rucksack. About the fabrics: The fabrics used for the Switch range were chosen specifically to make the Switch backpack cover extremely versatile. The reflective material used is the same as the highly popular REFLECT360 range and it is made from a mix of polyester and reflective beads and it is certified to CE EN 20471 standard. The fluorescent yellow side is made from 100% polyester with a waterproof PU coating. Waterproof | Fits most bags up to 35 litres | Elastic edges to secure a tight fitting | Two elastic straps to secure using poppers | Reversible: Fluorescent yellow / 100% reflective (CE EN 20471 certified)