The airlines are at it again. New “improved” seating is on its way. With no sustained similarity in coach-class seating between the major airlines, other than discomfort, the seat battle in the back of the plane focused on leather for the most part and, today, thin is in from the airlines’ point of view.

Tripso covered the introduction of a revolutionary new armrest design that begins to solve the problem of having the unfortunate soul stuck in the middle seat. However, who knows when those new over/under armrests will begin to be seen on aircraft. But there are other changes coming.

It’s lucky for American passengers that the Asian and European airlines still pay close attention to their back-of-the-plane seating, because eventually U.S. airlines have to catch up. The latest change is thinner seats.

The chance to help weary coach passengers is here. A number of designers are taking advantage of new technology to create thinner, but potentially more comfortable, seats.

The question is whether airlines take advantage of the technology to provide comfort and more space — or use it to put more seats on the plane. So far, the evidence is: both.

Since these seats might mean additional income for the airlines because of the ability to squeeze in another couple of rows of seats on many aircraft, chances are airlines will move more quickly with the thin seats before they invest in new armrests whose only function is passenger comfort.

To be fair, the profit motive for airlines is not only through squeezing in additional passengers, there is also a profit incentive because of the lighter materials used in these new thin seats. Less weight in aircraft mean a requirement for less jet fuel that translates directly to the bottom line.

American has introduced thinner seats that are said to provide an additional inch of knee space. AirTran has outfitted some 737s with new thin seats allowing them to add another row of seats in that aircraft while adding an inch of legroom — a win-win situation.

Air Canada, Frontier and Continental have new seats with a different recline structure and contour system that keeps seatbacks from crushing the knees of passengers when fully reclined.

Finally, headrests are changing, too. American has installed leather headrests and headrests with “wings” to make sleeping more comfortable. These new headrests have been installed through the entire fleet even in their tiny regional jets. Frontier Airlines has also installed “wings” with favorable comments from passengers.

So if your seat is feeling different, if you think you may have lost some weight, don’t be too smug. The weight loss and the new shape might not have anything to do with you. It just might be your thinner, trimmer, expertly-contoured and lighter coach seat.