The BMW tank top bag with part number 77498551736 is an official BMW Motorrad accessory specifically designed for the S 1000 XR motorcycle. This expandable tank bag is built with durable, waterproof materials for long trips and everyday riding. 
Features and specifications
Compatibility: This bag is designed to fit 2014-2019 S 1000 XR models (K49).
Expansion volume: The main compartment has an expandable volume, from 10 liters to 15 liters, for flexible storage.
Weatherproof construction:
The main compartment is fully waterproof with a roll-and-snap closure and taped seams.
It is made from polyurethane (PU) coated polyester fabric.
Pockets and compartments:
A water-repellent outer pocket, emblazoned with the BMW Motorrad logo, is useful for smaller items.
A transparent map pocket on top is also water-repellent and has a large access opening to the main compartment.