It's a bottle holder. It's an aero bag holder. No, it's the Super Wing!
The XLAB Super Wing is a rear hydration and repair carrier that offers all of the same features as their revolutionary Carbon Wing, just easier on the budget and slightly heavier. Constructed from aerospace-grade aluminum alloy, the Super Wing just may be the toughest carrier on the market. Easily allowing for water bottles in 3 different placements and 4 different angles, the Super Wing is a versatile carrier that tucks away inside the aero pocket created by your body cutting through the wind. With this hydration and repair carrier doing the work, you can save up to 13 seconds over 40 kilometers.