The Ear Cups
The QuietComfort ear cups are lined by very soft and pliable ear cushions. They are so comfortable that you can actually wear it for hours. Unlike ear cushions on other headphones, they don't make your ears sweat.
It could be that the ear cups actually cover the ears, instead of resting on them. Even then, the area around the ears on which the QuietComfort's ear cushions cover do not sweat even after prolonged use. These certainly are very luxurious ear cushions.
Although a good passive headset employs noise absorbing materials in the ear cup, the QuietComfort's ear cups appear to be made of nothing more than a single layer of plastic. This probably is how they cut down on its weight. But will this adversely affect its passive attenuation capabilities? We will find out later.
The ear cup
Take a closer look inside the ear cups. You will notice that there appears to be a tear in the speaker cover. Actually, the QuietComfort's speakers are not directed perpendicularly to the ear. They are actually canted at an angle that's directed to drive sound down the ears. Why?
Well, as mentioned before, the QuietComfort's ear cups cover the ears instead of resting on them. If their speakers point perpendicularly to the ear cups (like other headphones), then the sound waves will not be directed into the internal ear. Instead, they will be beating on the auricle. Other headphones are not affected by this because they rest on the ears themselves and thus are automatically positioned to send sound waves directly down the ear.
This means that the QuietComfort must be worn correctly. If you mix the proper position of the ear cups - left ear cup on the right ear and vice versa, you won't just get reverse balance like what you would expect with normal headphones. The sound perceived will actually be completely different from the actual sound reproduced by the headset! So, take note of the left and right markings Bose printed on the headband, just above the ear cups.