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A comfortable business jet cabin is important, of course, but a comfortable seat in that cabin may be even more essential. After all, that's where you'll spend most of your time aloft.

How can you measure a seat's comfort level? It's "a lack of awareness [of the seat]," suggested Mike Dennis, president and CEO of Oregon Aero in Scappoose, Ore. "The closer we come to a comfortable seat, the less feedback we get."

Achieving such comfort requires a marriage of technology and the human form, and to this end, aircraft and seat manufacturers have been devoting considerable effort in recent years.

Business jet passenger seats begin with a metal or composite frame and all the attendant mechanical and electrical equipment. The framework is usually then sent to the center that has been contracted to do the cabin completion or refurbishment. There, a combination of foams are cut and glued together to fit the frame. Next, the upholstery is cut, sewn and fitted.

Total customization isn't possible with seats destined for fractional or charter operations, since they may be occupied by 300-pound linebackers one day and 100-pound runway models the next. But airplanes in which at least one seat has been earmarked for a specific individual are a different story.

In such cases, the person's weight, body shape and proportion are major factors affecting the choices of foam for various layers as well as the seat's shape. The individual for whom the seat is being built may even come in for what manufacturers only half-jokingly refer to as the "butt test." If the person isn't available to come in, the seat may be shipped to him for approval before upholstery is applied.

FAA requirements-especially regarding fire-blocking qualities of the foam and a 16g-impact standard-are a challenge to creating more comfortable seats. To meet the impact standard, seats have to be able to withstand 16 times the force of gravity, and some manufacturers claim that this results in less comfortable seats than the old 9g standard.

While that is a matter of debate, experts seem to agree that leather seats are far more popular than fabric. "Fabric is less expensive, but among those buying a private jet, there is a predisposition toward leather," said Mitzi Mills, president of Anzea Textiles in Fort Worth, Texas. Cindy Halsey, vice president of interior design engineering and development for Cessna Aircraft, agreed, saying fabric is "virtually never" the choice of women, whose skin is more likely than men's to come in contact with the often scratchy fabric.

The best choice in leather is calfskin, said John Edelman, president of Edelman Leather of New Milford, Conn. "It is a little thicker, rounder and softer." The worst choice is "top leather," which is painted, he noted.

"There's nothing more comfortable than sheepskin, which is a standard upholstery product for pilot seats-a layer of cushion on top of the foam," Edelman added. The downside is that it isn't considered particularly attractive. It also needs frequent vacuuming, and the cleaning process requires shampooing.

Those who opt for fabric upholstery most often select jacquard, typically a durable blend of natural fibers with the pattern woven into it.

Business jet passenger seats employ urethane-base foams of differing densities, usually resulting in a cushion that is a little softer in the center and firmer along the sides. "You want to be sitting in it rather than on it," said Gary Palmer, vice president of operations for Skandia, a seating products specialist in Davis Junction, Ill.

Urethane-base foam may be the single most important factor in building comfort into the seat. One product recently finding favor with the seating industry is so-called "memory" foam. "It's only slightly more expensive than the top-end foams, but a comfort level that is significantly better," said E-A-R business development manager Brian Joyal.

While other foams give under pressure and adapt to the shape of the individual, they also push back. That continuous pressure for an extended period results in ischemia (a $10 word to describe a reduction in the flow of blood). "It's like applying a tourniquet to the skin," said Dennis, "and the resulting discomfort can manifest itself in as little as 30 minutes." It is this discomfort that can lead adults to squirm like six-year-olds.

The advantage of memory foam, which is both pressure and temperature sensitive, is that it yields to pressure, and as it warms, it assumes the shape of the individual human body. As a result, it no longer pushes back. It was originally designed for use by NASA and only in recent years has begun to find favor in the business aviation industry. Cessna Aircraft recently introduced a new seat as part of the mockup for a large-cabin project. The company drew heavily from the automotive industry's high-end seat-engineering experience.

The result is a research-and-development program in which the design team led by Gary Sauber is in essence "working backward." Rather than order a seat and do the foam buildup within that standard frame, Cessna is creating a foam buildup and then designing the framework around it. "We'll be saying, 'Here is the comfort outcome we want. Now build a frame to support it,'" Sauber explained.

Cessna and other companies are also pushing seat manufacturers to include features found in automobiles, such as heated seats and more refined electrical adjustments.