United's Economy-Plus seats: Instead of bulky foam cushioning, the airline's slim new coach seats will be padded with polyester.

United Continental

s rising fuel costs erode profits, United Airlines has come up with a claustrophobia-inducing way to boost income: Installing thinner, lighter seats onto some of its planes so it can cram in more passengers. Here, a brief guide we've managed to squish into less than a page:

How many more people is United packing in?
The seats, which United will begin installing next year, use a polyester padding — supposedly ergonomically superior to bulkier traditional foam cushioning. The new smaller seats let United add one row to the 12 to 15 rows in the economy sections of its 152 narrow-body Airbus jets. Net gain: Another six passengers per flight.

Does this mean passengers will have less room?
You'd think so. But United insists the change will give passengers more leg room. The smaller seats, made by German-based Recaro, will allegedly take up less space, increasing the amount of "living area" for each passenger's knees. But many frequent fliers remain pessimistic.

What are travelers afraid of?
"Having more people on a plane makes it less comfortable," says Alex Davies at Business Insider. "Boarding and unboarding takes more time, there's less space for carry-on luggage, bathroom lines get longer, food service (if there is any) is slower." Every change the airlines make to squeeze more people onto a plane, one traveler tells CNN, makes the cabin feel more like a "cattle car."

How much money will this make for United?
A lot, potentially. More passengers obviously increases ticket revenue. What's more, the new seats' lighter aluminum frames will decrease the planes' weight, says United CFO John Rainey, yielding "an appreciable amount of fuel savings."

Are other carriers packing in more seats, too?
Many European air carriers, including Lufthansa, Swiss, and Brussels airlines, have already installed Recaro's seats on their jets. Southwest and Alaska airlines will be switching to slimmer seats. And budget airline Spirit, which made a similar change in 2010, managed to pack in 33 more seats on its flights. Welcome to Sardine-ia.

Sources: Business Insider, Daily Mail, Los Angeles Times, NBC Chicago