I admit, I bought one that matched my bike.
If this is product design homework, know that you are on a well-beaten path. For a helmet to meet basic standards, the cushioning has to be thick enough to reduce the g forces to a sufficient level on impact. Thicker than that is safer. That's the primary influence on the silhouette.
Motorcyclists can get fashion helmets that are not up to code, and even fake DOT stickers that say they're ok, but this is usually to fake compliance to helmet laws. A cyclist is more likely just to leave it home.
Ladies have a lot more societal expectations of and for their appearance than men. They are expected to do their hair and makeup on their own time in their own home and arrive at work fresh as a daisy. That makes it more of a problem for them to exercise on the way to work and wear a helmet, or to use facilities at work men might take for granted, like a shower in a locker room.
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Genesis 49:16-17