It wasn't that long ago when a seat was just a seat. German cars had seats that were rock hard, and those in American cars were puffy overstuffed couches. Everybody else was somewhere in-between, and that was the limit of seating variety.

Now there are heated seats, ventilated seats, air-conditioned seats. There are seats that give you a massage, and knead your sore back. Coming soon are seats that help improve your posture and "active" seats that grip your body and hold you in place during hard cornering. Further out are seats that swivel 45 degrees so senior citizens and aging baby boomers can pour their stiff-kneed bodies in and out of vehicles more easily.

It's all aimed at giving consumers that warm, fuzzy feeling when they step into their car or truck - and selling them more high-profit options. Once they get a taste of some of these features, they're often hooked for life, and suddenly once-lavish frills turn into necessities. What's more, these pampering devices are migrating swiftly to lower-priced cars, so now even middle-income consumers can experience some of the perks once only enjoyed by the wealthy.

Leading this warm-and-fuzzy charge in North America are heated seats. Although common in Europe for decades, especially in frigid Scandinavia, only a decade or so ago Americans considered them a ridiculous frill for only the super-rich and quirky owners of Saabs and Volvos. Now, heated seats have migrated from the realm of the $90,000 S-Class Mercedes-Benz to the modest $20,000 Saturn L-Series. They also are available (usually as part of the leather upholstery option) on the Pontiac Grand Prix, Chrysler Concorde, a host of sport/utility vehicles (SUVs) and even a few pickup trucks.

That's not to say heated seats are finished carving out territory in the luxury market. Numerous high-line European cars are available with heated rear seats, as well as more heating options, such as the ability to keep the back of the seat warm while turning off the bottom cushion.

Heated steering wheels and side mirrors also are being added to the mix. U.S. luxury carmakers Cadillac and Lincoln, who began offering heated seats only recently, now have caught up and seem to be trying to make up for lost time by offering a variety of other customer-coddling features such as massaging seats.

Lear Corp. and Johnson Controls Inc., North America's dominant seat suppliers, say they don't specifically track heated seat installation rates. However, Robert Klein, marketing manager for W.E.T. Automotive Systems Ltd., North America's largest supplier of seat-heating components and modules, says business has tripled in the past few years. W.E.T.'s parent company, based in Germany, had $110 million in sales last year.

The demand for heated seats has grown dramatically in North America, Mr. Klein says, largely because it is following on the heels of the popularity of leather interiors. He says 25% to 30% of vehicles ordered with leather also have heated seats. Officials at Lear Corp. say that's partially because leather feels colder than cloth. But demand for heated seats isn't limited strictly to cold climates.

J.D. Power and Associates surveyed more than 87,000 owners of 1999 vehicles and found that just under 14% of all new cars and trucks now feature heated seats.But 28% of all vehicle owners said they would like the feature in their next car. Not surprisingly, 63% of luxury cars have heated seats, and 65% of luxury car owners say they want them in their next car.

But in North America heated seats are most popular on luxury SUVs: 83% have them. J.D. Power says owners of compact cars and pickups are interested in heated seats, too, but they aren't willing to pay much extra for them.

Next on the horizon are ventilated and air-conditioned seats that either push or pull air through the seat upholstery to eliminate that wet, sticky feel on hot summer days.

The first in production is currently available on the Saab 9-5. Saab claims it also was the first to introduce heated seats in 1971. The seat uses two electric fans in each front seat - one in the seatback and the other in the lower cushion - to remove warm air trapped between the person and the seat. The fans pull air through perforations in the leather upholstery and small channels in the padding and then vent it underneath the seat.

It sounds like a frill we could all live without, but then again, that's what everybody used to say about heated seats.