Break-In, a unique concept for bristles. Bristles are extremely stiff and stiff when new, but become slightly softer on exposure to water. After a period of use, the bristles repeatedly absorb water and dry, and the hair's microscopic structure changes. The signature change is that the bristle tips start to bifurcate. The bristle brush, while still stiff when dry, is no longer straight but spread out and becomes softer than before when it hits the water, making it "better with use."
Break-in refers to the process of artificially accelerating the brush. The main method of break-in is to grind and lather the bristles with a bristle brush and leave the bristles for half a day or a day without shaving or washing off the soap. Repeat several times to basically complete the break-in and remove the bad smell of the bristles. Some even put the bristles directly into the fridge when they are resting, supposedly to speed up the break-in process. Even if it's not a bristle brush, you can use this method to remove odors from other natural bristles.