Haze (Fogging) Determination for Automotive Interior Trim Components

Haze (fogging) determination for automotive interior trim components evaluates the tendency of volatile substances to evaporate from materials such as instrument panels, door trims and seat covers and to condense as a light-scattering film on cooler glass surfaces. Conducted by accredited third-party laboratories in accordance with ISO 6452, DIN 75201 and SAE J1756, the test supports material selection, supplier quality control and compliance with OEM interior air-quality specifications. This article explains the principle, sample types, test items, methods, acceptance criteria and typical applications of interior trim fogging determination.

Technical Overview

Fogging, often referred to as "haze" in automotive interior testing, describes the condensation of volatile organic substances released from interior trim materials onto cooler adjacent surfaces, most critically the inner face of the windshield. Under solar loading and elevated cabin temperatures, plasticizers, flame retardants, stabilizers, lubricants, residual monomers and other additives in polymers, textiles, leathers, foams, adhesives and coatings can evaporate and subsequently condense on glass that is significantly cooler than the emitting surface. The resulting deposit forms a milky, light-scattering film that reduces driver visibility, degrades glass gloss and clarity, and is difficult to remove, which is why fogging behavior is treated as both a safety and a quality attribute.

Fogging determination simulates this mechanism under accelerated, reproducible laboratory conditions. A conditioned specimen is heated inside a sealed glass beaker so that its volatile constituents evaporate, while a temperature-controlled glass or metal plate seals the top of the beaker and acts as the cold condensation surface. The condensed film is then evaluated either optically (reflectometric method) or by weight (gravimetric method). The two reference procedures are described in ISO 6452 and DIN 75201, with SAE J1756 and QB/T 2713 (for leather) providing closely related approaches. Accredited third-party laboratories routinely perform these tests as part of interior material qualification and vehicle air-quality programs.

Testing Samples

Rigid and Semi-Rigid Polymer Trims

Injection-molded or extruded components such as instrument panel substrates and skins, door trim panels, A/B/C-pillar trims, center consoles, glove box lids, air vents and decorative bezels made from PP, ABS, PC/ABS, TPO, PA, POM or PVC are tested in their finished, as-supplied state whenever possible so that process additives and surface treatments are captured.

Soft-Touch and Upholstered Materials

Seat covers and facings, headliners, door bolsters, armrests, steering wheel wraps, shift boots and sun visors based on PVC or PU synthetic leather, natural leather, textile fabrics and laminated composites are classic high-fogging-risk materials due to plasticizers, tanning agents and finishing chemicals.

Foams, Adhesives, Sealants and Coatings

Flexible polyurethane foams, hot-melt and solvent-based adhesives, butyl or acrylic sealants, acoustic insulation mats, lacquers and topcoats contribute significantly to cabin volatility and are therefore evaluated individually or as part of the trim assembly.

Elastomeric Components

EPDM weatherstrips, TPE and TPV soft-touch elements, rubber mats and similar elastomeric parts containing process oils and antioxidants are also common test candidates.

Specimens are typically cut as flat discs (commonly around 80 mm in diameter) from the finished part or from a representative plaque, with the functional surface facing upward. Unless otherwise specified, samples are conditioned in a standard atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity (ISO 291) before testing, and loose particles are removed without altering the surface.

Testing Items

Depending on the specified method and the applicable OEM or material specification, the following results are reported:

• Fogging value (reflectometric), %: the ratio of the reflectometer (gloss) value of the glass plate after fogging to its value in the clean state, multiplied by 100; higher values indicate lower fogging tendency.
• Condensate mass (gravimetric), mg: the mass of volatile matter deposited on a preconditioned aluminum or glass target, weighed on a microbalance to 0.01 mg; lower values indicate lower fogging tendency.
• Supporting observations: visual assessment of the deposit (oily, waxy or crystalline), gloss retention of the condensation plate, and, where required, supplementary total volatile organic compound (TVOC) screening of the same material to support root-cause analysis.

Typical acceptance criteria cited in automotive specifications are a fogging value of at least 90 % (frequently 95 % or higher for glass-adjacent parts) for the reflectometric method, or a condensate mass not exceeding approximately 2 mg for the gravimetric method; the exact limit always follows the governing specification.

Testing Methods

Specimen Preparation and Apparatus

A flat specimen is placed in a clean, flat-bottomed glass beaker closed by a sealing ring. The beaker is immersed to neck level in a temperature-controlled heating bath (glycerol or oil, stable to within about ±1 °C), while the top of the beaker is closed by a cooled plate through which water at 21 ± 1 °C is circulated. The temperature difference between the hot specimen surface and the cold condensation surface drives the evaporation-condensation cycle. Blanks and, where specified, reference materials are run in parallel, and all glassware and target plates are scrupulously cleaned and preconditioned before use.

Reflectometric Method (Method A, ISO 6452 / DIN 75201-A)

The specimen is heated, typically at a bath temperature of 100 °C for about 3 hours, while the condensation surface is held at 21 °C. Volatiles deposit on the cooled glass plate within a defined central area. The reflectometer value (gloss) of the glass plate is measured before the test, after conditioning and again after the fogging exposure, using a defined measurement geometry (commonly 20° or 60°). The fogging value is calculated as the percentage ratio of the fogged reflectometer value to the clean reflectometer value. This method correlates directly with the visual impairment caused by the deposit on glazing.

Gravimetric Method (Method B, ISO 6452 / DIN 75201-B)

A preconditioned, accurately weighed aluminum foil or glass target serves as the cooled condensation surface. The specimen is heated, commonly at about 95 °C over an extended exposure (frequently cited as approximately 16 hours), with the cooling plate again held at 21 °C. After exposure, the target is reconditioned and reweighed, and the mass increase represents the condensed volatile matter. Exact temperatures and durations are selected in accordance with the referenced standard or the applicable specification. The gravimetric method quantifies the total evaporable fraction and is particularly useful for comparing formulations and additives.

Related and Supplementary Procedures

SAE J1756 describes a comparable fogging determination used widely in North American supply chains, while QB/T 2713 covers the fogging characteristics of leather. For transparent or translucent interior and glazing components, light-transmission haze per ASTM D1003, ISO 14782 or GB/T 2410 is a distinct optical property and should not be confused with the condensation-based fogging test described above. Many interior air-quality programs combine fogging determination with odor and VOC emission testing to give a complete picture of cabin volatility.

Applications

• Material and supplier qualification during vehicle development, including approval of new resin grades, plasticizers, foams, leathers, textiles, adhesives and coatings.
• Incoming and serial production quality control to verify that fogging behavior remains consistent across batches and manufacturing sites.
• Engineering change validation, such as substituting a low-volatility plasticizer or modifying curing conditions for polyurethane foam.
• Root-cause investigation of field complaints involving windshield haze, film build-up on glazing or instrument cluster covers.
• Comparative benchmarking of competing materials and support for regulatory and voluntary interior air-quality requirements.
• Documentation for customer-specific material data sheets and engineering specifications throughout the automotive supply chain.

FAQ

What is the difference between fogging value and optical haze?

Fogging value measures the amount of volatile matter that evaporates from a material and condenses on a cooled surface under accelerated conditions, whereas optical haze (ASTM D1003, ISO 14782, GB/T 2410) quantifies wide-angle light scattering transmitted through a transparent specimen. The two properties are unrelated and require different test setups.

Which method should be selected, reflectometric or gravimetric?

The choice follows the governing specification. The reflectometric method best reflects the visibility impact of deposits on glass and is preferred for glazing-adjacent components, while the gravimetric method gives an absolute mass of condensable volatiles and is often used for material comparison and formulation development. Many programs require both.

What are typical acceptance limits?

Commonly cited requirements are a fogging value of at least 90 % (reflectometric) or a condensate mass of no more than about 2 mg (gravimetric); tighter limits may apply to parts located near the windshield. The applicable OEM or material specification always takes precedence.

What causes a material to fail the fogging test?

Frequent causes include high levels of plasticizers, insufficiently cured polyurethane systems, residual solvents or monomers, low-molecular-weight process oils, over-loaded stabilizer or flame-retardant packages, and inadequate post-curing or drying of coatings and adhesives.

How should samples be submitted for testing?

Finished parts, representative plaques or flat cut specimens with a minimum area covering the beaker opening should be supplied in clean, inert packaging that cannot transfer contamination. Laboratories typically require several replicate specimens per condition along with material identification and the target test method or specification.

Can fogging testing be combined with other interior air-quality tests?

Yes. Accredited third-party laboratories commonly perform fogging determination together with odor evaluation, formaldehyde screening and total VOC or semi-VOC emission testing to provide a consolidated assessment of cabin air quality compliance.