I get that the green/upper bar stands for breast size but what does the kower bar mean? Softness? Perkiness?

Maybe the size/tightness of her clothing?

Tsuchino said:

I get that the green/upper bar stands for breast size but what does the kower bar mean? Softness? Perkiness?

A good point of comparison is the second and third image, since the bust size barely changes, but the robe does. It changes the size of the chest area on the robe, so in the fourth, where there's no breasts but medium robe size, it's really baggy, but the fifth has large breasts shrink-wrapped for impossible clothes.