The shape of mugs like bamboos. It can save place when you stacking them. And the side of mug can be tied tea bags.
This mug is made of bamboo and ceramic. In the chinese culture, the bamboo is a symbol of humbleness. Stacking mugs means that you will be blessed and it will bring good luck to everything undertaken. To always reach higher and bring the best. This can also be very convenient to save place. The side of the mug with a salient effect can be used to tie tea bags on it.