The new models in Sennheiser's HD2xx series of headphones are designed to provide a closed-back alternative to the company's well-regarded PX100 headphones. As you probably know, closed back designs have two major advantages over their open-back fellows. First, the cups in a closed back design resonate and reflect the lower sound frequencies back into the ear and cut down on leakage, which can result in a more pronounced bass. Second, less sound leaks out or in through the headphones so you get less background noise, and can listen to your headphones at a slightly lower volume, while those around you aren't forced to enjoy your favourite beats.
Now, Sennheiser already does several excellent pairs of closed-back headphones suitable for portable use, but the HD218s are the first I've seen that seem designed specifically with this in mind. Taking some design cues from the company's high-end HD5xx series, the 218s are extremely compact, and the earcups twist such that you can pack the headphones flat for easy transport. The slimline cable dangles from the left earcup, minimising tangle, and the whole package weighs a mere 80g.
Despite this, build quality is up to the manufacturer's typical high standards. The plastics don't feel horrendously cheap, the joints feel solid, and if the cable is a little weedy by Sennheiser standards, it's well-protected where it meets the earcup and the plug. What's more, the HD218s come backed up by a two-year guarantee.
The PX100s are one of the most comfortable pairs of portable, over-the-ear headphones I've tried, and the HD218s aren't far behind. The light weight helps, as does a forgiving adjustable headband with a generous leatherette pad for the top of the head. The earcups, meanwhile, offer comfortable padding of the same material across the inner surface, with a circular cloth grill just below centre to give the output a path to your ear.
These are seriously comfortable ‘phones, and even with no sound coming through they do a reasonable job of muffling outside noise. You can still hear what's going on, but a little of the edge is taken off. With the sound turned up you don't get quite the same level of isolation you would get with fully circumaural headphones, but there's less leakage in both directions than you'd get from regular, open-back portable 'phones. Note that this doesn't mean ‘no leakage'. Enough sound still gets out to annoy anyone sitting next to you, so don't push the volume levels too far if you're out on public transport and don't want to annoy other passengers.