Upgrading the brake fluid caps on a BMW S1000RR is a popular modification that uses CNC-machined billet aluminum caps to replace the stock plastic covers. These caps are available for both the front and rear brake fluid reservoirs and are designed to provide both an aesthetic enhancement and a secure seal. 
Features and types of aftermarket caps
Material: The most common material for these caps is high-strength 6061-T6 aluminum, which is both lightweight and durable.
Finish: Caps are typically anodized for a hard, corrosion-resistant, and vibrant finish. This finish prevents rust and oxidation.