Why a girls' bra and not a women's?
Girls' bra guide
So what makes a girls' bra a girls' bra and not a women's bra? The difference isn't in name only—girls' bras are actually designed differently from women's.

Easing into it
Some girls may want to wear a bra, but that doesn't mean they want to scream it from the rooftops. Nike girls' bras are designed around real insights from real girls, which is why some styles feature super-skinny straps and U-shaped necklines. These designs make it easier to wear a bra under a T-shirt or tank top without being too noticeable.

Targets sweat
By comparing girls' and women's sweat patterns, Nike bra designers pinpointed the high-sweat areas on the body and strategically placed breathable mesh panels or other sweat-wicking elements in the bra. That way, at any and every stage, there's a Nike bra to help keep things dry and comfortable.
All about comfort
There isn't a certain age where girls start wearing women's bras—it all comes down to comfort and performance. If girls' bras aren't providing complete support, it may be time to transition to a women's bra.