The brush is 41 cm long, the bristle area is 12 cm long and has a 6 cm diameter. This brush is suitable for bottlenecks of 16 mm and can be used to clean both the neck and the base of your bottles. Bristles are made of light sanitized and fully compostable pig hair, but don't worry, there is no animal cruelty involved in its production (similar to shaving a sheep for its wool). The metal handle can be recycled.
I use it mostly to clean my square oil and vinegar bottles as it is particularly suited for bottles with a narrow opening, but you can clean any bottle with it including your stainless steel water bottle. A solid and durable product that is completely plastic free. It is manufactured sustainably in Germany by an ethical family business.