Luffa is a genus of tropical and subtropical vines in the cucumber family
In Japan, it is called hechima (へちま) and is cultivated all over the country during summer. It is commonly used as a green vegetable in traditional dishes of the Nansei Islands and Kyushu while other regions of Japan grow it predominantly for use as a sponge or for applying soap, shampoo, and lotion.
This kind of soap making is very popular nowadays, as the soap contains the sponge, making it easier and faster the cleaning process. Also it is very soft and feels like heaven using it.