Most headphones are open, meaning they have a mesh or something on the outside and not a solid "wall".

"Open" indeed means that others will hear the sound - and you will hear the noises from the outside.

I thought it's good mentioning more of the closed phones - so one can enjoy the music in noisy spaces some more. And save your ears in the process, since you don't have to turn the volume to eleven to get a good sound.

One of the most common disadvantages of closed phones is that they don't provide a good soundstage, meaning the instruments are not located as 3-dimensional in space as with open phones. But isolation is more important than soundstage when you're on the move, IMO.

If you want the best in open design, don't look further than the $10 KSC75

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