What Are the Applications of Semi-Rigid Polyurethane Foam in Automotive Interiors?

The automotive dashboard is a fixed panel that holds instruments, radios, air conditioning switches, heaters, and various lighting switches. It consists of an outer skin, semi-rigid polyurethane foam filler, and a metal framework, serving both decorative and aesthetic functions. The excellent shock-absorbing properties of semi-rigid polyurethane foam make it an important safety component in vehicles. Commonly called shock pads or cushioning dashboards, they protect passengers by absorbing energy during impacts. Foam materials in the cushioning panels absorb and disperse the energy when passengers collide with the dashboard, preventing serious injury. Previously, dashboards made from metal sheets easily caused injury. Now, PU semi-rigid foam is molded inside an outer skin made of textured PVC or ABS thick film (0.8–1 mm).

The manufacturing process includes:

1.Heating and vacuum forming the thick film, then placing it into the mold.

2.Bonding the metal framework with the pouring mold.

3.Injecting foam raw materials with a foam machine for molding and foaming.

Applications of semi-rigid polyurethane foam have expanded beyond passenger cars to heavy trucks and buses to improve safety and comfort. PU semi-rigid foam fillers come in general types and room-temperature curing types. Other automotive parts made from PU semi-rigid foam composites include armrests, small storage box lids, curved parts, under-car mats, pillar and door covers, steering column pads, and shock pads. These products absorb shock because the open-cell semi-rigid foam expels internal air under compression, which is then refilled by the outer ABS or PVC thick film. When pressure increases, the tough foam cell structure deforms to absorb shock.

Due to its sound-absorbing properties, semi-rigid polyurethane foam is increasingly used in automotive floor mats, especially for buses and large trucks. These mats are produced using either prepolymer or one-shot systems. For very large mats, like those for trucks and buses, the prepolymer method is preferred for its good chemical flow properties. The foam bottom is generally covered with PVC or PE film for moisture and dampness protection.

The steering wheel structure includes a steel frame inside and an outer skin of integral PU semi-rigid foam. Made by reaction injection molding (RIM), it has a tough, dense outer skin and a honeycomb inner core, with skin thickness ranging from fractions of a millimeter to 5 mm. The skin density is 1000–1200 kg/m³, and the core density is several hundred kilograms per cubic meter. The skin and core form a continuous, smooth, soft surface protecting the foam core from mechanical damage. PU steering wheels provide comfortable touch, high functionality, and some impact resistance. The steering wheel center is a critical impact area for the head and chest; most passenger cars have padded steering wheel rims, making the steering wheel a key internal safety part.

Bumpers are external safety components made with high-density integral PU semi-rigid foam (density 1100 kg/m³). After an 8 km/h frontal impact, these bumpers return to their original shape, protecting vehicle parts such as headlights, doors, engine hoods, fuel, and cooling systems from damage. Bumpers and mudguards can also be made using glass fiber-reinforced polyurethane foam via reinforced reaction injection molding (RRIM).

Mudguards are thin, complex-shaped parts requiring mud, stone impact resistance, high impact tolerance, and reliable performance at -40 to 160 °C, making manufacturing difficult. Some mudguards use reinforced rigid foam structures.