The spring in the cup is used to shake it evenly when you need to make coffee or other powdered drinks. The spring in the cup is also called a rocking ball. The rocking ball in the water cup plays the role of stirring. When solid drinks such as milk powder and whey protein are added into a cup and shaken with water, it is easy to agglomerate or melt incompletely. Springs can help solid drinks melt and prevent caking.

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