Have you ever wondered why some people put a "wristband" on the brake oil jug, and are they afraid of freezing the weather? In fact, this practice began to appear in the late 80s, the practice of wrapping cloth on brake oil jugs. This thing seems to be called by foreigners: reservoir tank sock cover, which translates to probably "reservoir sock cover", which in our opinion is similar to the wristband used to play basketball.
However, in recent years, this practice has become less and less common on commercial vehicles, but many MotoGP machines are still in use, and they are certainly not just decorative. When playing basketball or tennis, this wristband has a sweatproof effect on the arm. On motorcycles, the reason for installing it on the brake oil pot is also similar, in order to "prevent brake fluid from exposing".
According to references, the brake fluid in the oil jug has a strong permeability and can easily damage the paint due to the nature of the brake fluid. Therefore, even if the lid of the oil pot is tightly closed, it may still leak a little, but it will not leak to the point of dripping water, unless something goes wrong. Another reason is that due to the nature of certain materials, brake fluid can corrode the oil jug, and even a small amount of brake fluid can lead to a significant loss of visibility if it comes into contact with the vehicle's windshield or helmet lenses.
If the wind pressure is propagated at a speed of 300 km/h, even a small amount of bubble-like adhesion can become a serious problem. That's why the car takes every possible measure to absorb the brake fluid that the oil cup may secrete through this cloth cover. However, it is also said that it is to prevent long-term exposure to ultraviolet rays from causing the brake oil from deteriorating, and it is also said to protect the brake oil pot from bumps.
All in all, various statements seem to have their own truths, but now fewer and fewer people use this, because after wearing the "wristband", people who feel good-looking are a minority, and with the advancement of technology, the problems that needed to be worried about before have been slowly overcome, and this practice seems to have gradually become a feeling.