An interesting article in fastcodesign.com talks about social science research into what makes one thing seem “cool” and a similar thing not.
Cool is a perception, not an inherent quality. It’s established in a very social process wherein a society’s trend setters adopt it (who determines who the trend setters are?), then it’s taken up by the majority.
The key to Cool is that it diverges from the norm, but not to the extreme. There is a boundary that can’t be crossed. Cool lies in the middle between not too conventional and not too controversial.
Cool is also a moving target. As something that is considered cool is adopted by the majority, it loses its cool-factor.
To design for Cool, you need to first know what the audience considers normal, then what they consider to be the limits of abnormality.