Up to 90% noise reduction, compact and foldable. Talk through button lets you communicate with others without having to remove the headphones.

After doing a lot of research comparing various noise-canceling options, I decided I wanted a pair of Sennheisers due to construction quality and the fact that they can be still used for listening even if the battery is out. I settled on this PXC 310 model over the larger 350s because I prefer to pack light and was willing to sacrifice a little noise-cancelling in favor of that.

The headphones have really good noise cancellation for on-ear phones, which I used both on airplanes and buses. Sound quality is quite good (although noticeably better with noise-cancelling on). No hissing sounds. They are comfortable for several hours of travel, although admittedly, after about 6 hours my ears started to get a little sore. I was able to continue to wear them though.

These come with a nice pouch to store the headphones while folded up. The AC charger for the lithium-ion battery comes with several adapters for use in different countries (this was cool). It's also nice that the AC charger is combined with a USB charger. If you have access to your computer this means that you can ditch the AC charger (which someone else's review called bulky -- I don't think it's that bad) and just charge it with the USB to micro-USB charger that is included).

The blinking LED on one side while noise-cancellation is on is nice to have so that you remember to turn it off, but people around you might find it annoying.

The sound is fine, but this is an earphone made for travel that requires a bulky re-charger for the noise-cancelling battery. That charger requires an interchangeable plug, for each country you visit. Bulky and I lost the USA plug almost immediately. Finally, the wire connecting the earphones to the Ipod is ultra-skinny. I caught it on a chair and it snapped. These are totally unnecessary problems.

I upgraded from the Sennheiser PXC-300. From a practical standpoint it's so much better not to have the noise cancelling unit separate from the headphones. It was always getting in the way. The battery door got broken on mine as well. Compared to the other model, the sound is much better as well (richer, less synthetic). The headphones are also very comfortable although I didn't think so at first; perhaps I broke them in. Charging over USB is also a nice plus.

Areas I would love to see change:

1) Headphone band is a little on the short side. If you have a big head, you may not get a good fit
2) The USB plug on the headphone is not a standard mini-USB connector but a proprietary jack. You may want to order a spare cable
3) Most annoyingly, the noise cancelling feature stays on even when the detachable audio cable is unplugged. If you don't remember to manually turn off the headphones, you will find the battery discharged the next time you try to use them.
4) I wish you could disable the blinking red light on the right headphone.
5) I want a shorter 2.5mm to 3.5mm cable so I can use an iPhone mic/remote.
6) The headphones (like the PXC-300) require a fair bit of output power to play. On the iPhone I am often near maximum volume.

I bought these to use on a recent JetBlue flight, and because I now have to fly for work a few times a year. The plane was packed with little at least 7 screaming kids. Although the headphones didnt completely remove all the screaming, it reduced the noise down way more than enough so that it became just low background sounds, and plugged in to the in-flight tv I didnt have to turn the volume up extra loud to hear the tv or to drown out the noise. I was more than satisfied with the results. It also did a great job of silencing the rest of the airplane engine noise too. All in all I was a little concerned up front about paying $200 for these and figured I would try them out once before deciding whether they were worth it. But that one 4 1/2 hr flight convinced me these are a keeper. They fold up nice and small, fit into a nice carry case that comes with the headphones, and use the same size charger as a Blackbery Storm II, so I only have to take that one charger with me on trips instead of two.

I had the possibility to compare side by side with a co-traveller using Bose; the Sennheiser giver the better sound and noise reduction.