The materials inside a vehicle influence its cabin air quality as well as its comfort and finish. Zotefoams‘ Sam Norman explains how early material selection and established testing can help manufacturers reduce avoidable emissions and the risk of costly design changes.
The “new-car smell” is a familiar part of buying a vehicle. It comes from compounds released by cabin materials, making it one aspect of interior design that manufacturers can influence through material choice. Assessing those emissions early can help improve cabin air quality and avoid costly changes later in development.
Plastics, rubber, textiles, leather, padding and adhesives can all release volatile organic compounds (VOCs) into the enclosed cabin. A 2024 study identified VOCs from interior materials as the main contributors to the familiar scent.
Establishing what those emissions mean for occupants requires both chemical analysis and odour testing. Chemical analysis identifies the substances present and their concentrations; odour testing assesses the sensory experience. Some compounds can be detected by smell at very low concentrations, so odour alone cannot establish a health risk. Any health assessment must also account for the duration and frequency of exposure.
For development teams, the practical task is to use that evidence to reduce avoidable emissions while maintaining each component’s required performance. Assessing options before materials and suppliers are fixed gives teams more scope to make improvements. Those decisions need to reflect how materials will behave in the finished vehicle.
Testing materials under realistic heat exposure
Heat exposure is an important part of that assessment. The 2024 study monitored one new car over seven summer working days and analysed 12 common VOCs. Its modelling identified material surface temperature as a more important influence on cabin VOC concentrations than cabin air temperature.
During the tests, average material surface temperatures ranged from 24.1°C to 64.2°C. Although the findings relate to one vehicle, they illustrate why material testing needs to account for the temperatures reached after a car has been parked in direct sunlight.
That assessment needs to cover the complete interior. A vehicle cabin combines substrates, foams, coatings, adhesives and finishes, each with its own VOC and odour profile. Heat can change the rate at which compounds move from those materials into the air, while the size and location of each exposed surface affect the overall result.
Assembly testing helps capture those combined effects. Seat foam is bonded to upholstery; headliners, carpet underlay and door trim can combine several layers. An individual material can perform well in isolation, while adhesives, coatings and other materials contribute additional emissions in the finished component. Specification should account for the likely temperature, exposed surface area and position of each assembly in the operating vehicle.
Testing before the specification is fixed can reveal excessive VOC emissions, unacceptable odour scores or fogging, where semi-volatile compounds condense into a film on glass. Identifying these issues early gives teams time to investigate the sources and assess alternative materials.
Replacing an automotive material late in development can be difficult. A substitute may need new supplier approval, component validation and production trials, while the required grade or quantity may not be available when needed. These delays can interrupt supplies to vehicle manufacturers, add testing costs and put production schedules at risk.
Using established tests to guide material choices
The industry already has established methods to support these decisions. The ISO 12219 series covers the measurement of vehicle interior air and emissions from cabin materials and components. These methods provide evidence for material selection and validation; the relevant acceptance criteria come from applicable regulatory requirements and original equipment manufacturer (OEM) specifications.
ISO 12219-1:2021, for example, specifies whole-vehicle chamber testing. Its methods include an ambient mode at 23°C to 25°C, an elevated-temperature parking mode for formaldehyde measurement and a driving mode that simulates a journey after the vehicle has been parked in the sun. This allows teams to assess cabin emissions under defined conditions relevant to vehicle use.
Alongside these measurement methods, OEM specifications can set requirements for individual substances and total VOCs, sensory odour ratings, and the tendency of semi-volatile compounds to condense on glass. These categories answer different questions. Chemical measurements establish whether specified emissions limits are met, odour scores capture the sensory experience, and fogging tests assess deposits that can affect cleanliness and visibility.
Meeting applicable regulatory and OEM requirements is essential. Manufacturers can also assess opportunities for further improvement against their own cabin comfort and quality targets. Component results contribute to that assessment, while validation of the complete interior establishes how the combined materials perform in the finished vehicle.
To assess those opportunities, development teams need comparable evidence for the materials under consideration. Comparisons should use the same test method and conditions, with clear information about the grade and sample preparation. Testing components and assemblies can then establish how the chosen materials perform with the adhesives, facings and other materials used in production.
Choosing materials for the complete cabin
Emissions are one part of material performance, so any proposed change must also meet the application’s requirements for durability, weight, thermal behaviour and acoustics. Cost and manufacturability influence what is viable. Considering these factors together allows teams to judge where emissions can be reduced while preserving the component’s function.
For foams used in seals, gaskets, ducting and noise, vibration and harshness applications, that balance depends on the polymer, additives and manufacturing process. Any adhesive or facing in the final component must also be considered.
Zotefoams’ range of high-performance materials includes foams that offer low VOC emissions and low fogging for automotive interiors. Materials expanded using temperature, pressure and nitrogen, without chemical blowing agents, are among the options manufacturers can assess against the requirements of each component.
For each application, manufacturers should compare results for the specific grades under consideration and validate the chosen material in its finished form. Early collaboration between material suppliers, converters and vehicle manufacturers gives teams time to resolve trade-offs before production commitments are made. It also gives them a clearer basis for specifying materials that support their cabin air quality targets and perform reliably in the intended application.
About the author
Sam Norman is head of business development for transport and smart technologies at Zotefoams, a global foam manufacturer whose advanced foam materials enable lightweight, high-performance applications for globally recognised brands such as Boeing, Airbus and Nike.
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