Why a seat resists your weight
A car seat is shaped to support a body that is moving, not simply to feel soft while you sit still. If the cushion lets you sink deeply, your hips can shift and your posture can slump. Firmer foam pushes back more evenly, helping keep you in a stable position and reducing the feeling that you are sliding around as the car accelerates, brakes, or corners.
That firmness is a compromise, not a measure of quality by itself. Foam that is too hard can create uncomfortable pressure points; foam that is too yielding may stop supporting you effectively. Seat designers have to balance cushioning, support, durability, and the space available in the cabin.
What the bolsters are doing
The raised edges along a seat’s cushion and back are called bolsters. In a turn, the car changes direction but your body tends to keep moving in its previous direction. A bolster gives your thighs or torso a surface to press against, limiting how far you shift and reducing the effort needed to brace yourself.
Bolsters are not a substitute for a seatbelt. The belt is the primary restraint in a crash, and the seat helps keep you positioned so the belt and other safety systems can work as intended. A seat that holds you steadily can also make ordinary driving less tiring: your muscles do not have to correct your posture as often.
The comfort you notice after the showroom
Showroom seats are often judged while the car is parked, when there is no cornering force and little reason to brace. On the road, that same shaped support has a practical job. The ideal seat feels forgiving under your body while still keeping you from settling into a loose, sliding posture—a distinction that plush upholstery alone cannot show.
