Are you sitting comfortably?

Lightweight, space-saving, durable seating – and comfortable too? Tapis Corporation’s sales director, Matthew Nicholls explains how science makes it all possible.

As seating manufacturers innovate and build new, thinner seats that can increase the density of a typical aircraft cabin, the focus has now turned to the question of whether we can make these thinner, lighter seats more comfortable?

The answer is yes. By observing what causes discomfort and applying the scientific method – what we call ‘comfort science’ – we can design seating that is lighter and smaller, but is actually more comfortable.

In using the comfort science approach to aircraft seating, the first thing we review is the human factor – how do our bodies support us when we sit? Evolved as hunter-gatherers, the human body was fundamentally not designed for sitting. As a race, humans are also growing taller and, more importantly, straighter in the way we hold ourselves. This affects the loads and strains the body is under when we sit.

We should think about the body as having three key elements, bones, muscles and organs, where organs include skin and all other components that are neither bone nor muscular. Bones are the framework or scaffolding for our bodies. They can support the greatest loads and do not tire after prolonged use. Muscles, on the other hand, need to be kept moving. When muscles are held in either an extended or compressed configuration for a prolonged period of time, lactic acid builds up as a trigger to tell the person to relieve the tension. For that reason, it becomes uncomfortable to sit in a muscularly tense position for a long period of time.

More than a feeling

When we sit, we principally sit on two bones, known as the ischial tuberosities or sit bones. The sit bones are part of your pelvis and form a triangle with your coccyx when you sit. When you sit upright, your back and upper body are neatly supported by your spine. The bones in your vertebrae are fully capable of supporting you, but only as long as you sit upright. If you start to slouch and move your spine out of alignment, your muscles start to take over to compensate and you start to feel more discomfort as your muscles inevitably tire.

Another key area of discomfort is your core body temperature and the feeling of wetness. The human body is very sensitive to temperature and maintains a very specific temperature. The optimum temperature for sleeping, for example, is 65°F and even small variations of 5°F or less can have a discomforting effect that can cause you to wake from your slumber.

When you move outside of your core body temperature it triggers another variable that increases the discomfort – that of wetness. When we sit for too long in the wrong temperature, we perspire to mitigate the effect, and, in turn, we start to feel wet. The feeling of wetness is one of the factors that passengers attribute to discomfort. It triggers an autonomic nervous system response in your body and decreases your core body temperature.

Put your back into it

Now that we have established the roots of discomfort in seating, we can work to address the problems. Our answer to creating comfortable aircraft seats centres around the concept of several key factors.

The first is to make sure that the human body is supported by the skeleton. To do this, we need to ensure that the spine is aligned vertically and that our heads are aligned vertically over the vertebrae of the neck. The pelvis should be in a neutral position, not slouched, and the knees should be at right angles to the thigh bone. To do this, it is vitally important that the height of the seat bottom is correctly angled so as to ensure the passenger’s knees are in equilibrium and at right angles to the thigh and shin.

Seat bottom cushions are principally made of foam, which has a measure known as the ILD or Indentation Load Deflection. This measure shows how much compression a foam will take under a given load. If we estimate the load for a 55-year-old male, we can soon see how much height loss there will be from the given load. Our aim is to suspend the passenger just high enough to ensure they do not sit on any of the hard points, such as the horizontal cross member tubes or the seat pan. If the cushion height is, say, 3.5” high, we should ensure that the passenger remains suspended a minimum of 0.75” above the seat floor. This will avoid the passenger ‘bottoming out’ and landing on the hard surface below.

Advanced seat covers, such as the those made with Tapis’ Ultraleather, achieve this with an inbuilt foam layer, which puts a little more height back into the equation and also decelerates the load. The speed or force at which foam compresses dampens the downward force that is applied on the top of it. So, the more foam you have, the more you dampen the passengers load downwards into the cushion, keeping them suspended a little higher up and preventing the passenger bottoming out.

Another aspect to consider is what ergonomicists call ‘maximum body contact’. This is a way to describe distributing the load across as much surface area as possible. Since pressure equals force divided by area, any increase in area, will result in a corresponding decrease in pressure, and a corresponding reduction in discomfort. The use of memory foams are useful in achieving this.

The takumi four-layer construction process used in Tapis’ Ultraleather consists of a foam layer and top skin, which conforms well to each passenger’s unique body profile. The top skin is extremely soft (but durable) so again it will conform or follow the body’s shape more consistently, meaning it will have more surface level contact with the body, increasing area and reducing pressure.

Like flying in the home

For temperature control, breathable seat cover material is a major influencing factor. This is the reason why flying in polyester track pants has less perceived comfort versus lightweight cotton pants. The cotton material is cellulosic in nature. Cellulosic fabrics are extremely efficient at retaining water vapor, keeping it away from the body, which is why they’re used so extensively in workout clothing.

This is also the reason why heavily pigmented leathers are often perceived as hot and sticky. Their sealed, heavily pigmented top coat is not breathable and causes the perspiration to pool and remain in contact with the passenger’s body, increasing their perceived discomfort. That’s why fabrics are used so extensively in long haul aircraft cabins, as they have the highest breathability of seat cover materials.

Tapis’ Ultraleather Brisa product is a particularly unique innovation in this regard. It has similar breathability to fabrics and has a rayon backcloth, which is cellulosic in nature. The combination of breathability of the microperforated holes and the water absorbency of the rayon backcloth make it comparable to fabric in terms of comfort but as maintainable as leather, without the need for dry cleaning.

The last several years have seen the aircraft interior industry make great strides in achieving new levels of comfort for passengers, while taking up less space and weight. By applying the ‘comfort science’ methodology to seat design we have a better understanding of what causes discomfort and how to counter its effects as airlines strive to keep weight down and maximise the use of available space.