Solar Reflection and Thermal Behavior of Daimler PAPP PWT 7333 Automotive Materials

The “Daimler PAPP PWT 7333 Heating Behavior of Materials” standard, developed by the Daimler-Benz automotive company, describes a procedure used to evaluate the thermal behavior and surface reflectivity of materials exposed to sunlight, particularly leather and interior upholstery components. As part of a material qualification system for automotive interiors, this standard is especially important for premium vehicle interiors where cabin comfort, thermal management, and color stability are critical performance factors.

Daimler PAPP PWT 7333 is a material testing specification relating to:

• Surface reflectivity measurement
• Solar heat absorption behavior
• Indoor material temperature increase under sunlight
• Evaluation of leather and leather fiber materials.

Modern car interiors can overheat in direct sunlight. Dark-colored materials, in particular, absorb near-infrared radiation, leading to the following:

• High surface temperatures
• Passenger discomfort
• Increased air conditioning load
• Faster material obsolescence.

This standard is designed to measure how much solar energy a material reflects and how much it absorbs. Materials with higher reflectivity generally stay cooler when exposed to sunlight. The described test method measures the surface reflectivity of materials, typically in the near-infrared wavelength region.

The general methodology includes the following:

• Preparation of material samples
• Exposure to controlled light or infrared radiation.
• Measuring reflected energy using spectrophotometric equipment.
• Calculation of reflection properties
• Assessment of thermal behavior

This method is commonly applied in the following cases:

• Skin
• Leather fiber composites
• Interior furnishing materials
• Polymer surfaces
• Coated internal components

Generally, this standard is listed alongside other automotive original equipment manufacturer specifications, such as:

• BMW PR 358
• DIN EN ISO 17502
• Mercedes DBL standards

Many accredited laboratories describe the test as similar to solar reflectance measurements at approximately 980 nm infrared wavelength. This suggests that automotive manufacturers use similar approaches to manage cabin temperature and passenger comfort.

The thermal behavior of automotive materials refers to how materials inside and outside a vehicle absorb, retain, and release heat when exposed to sunlight or high temperatures. This property is extremely important in vehicle engineering as it directly affects comfort, safety, durability, and energy efficiency. For example,

• Passenger comfort: One of the most obvious reasons is cabin comfort. Interior surfaces, such as seats, the steering wheel, the instrument panel, and door panels, can become excessively hot after exposure to sunlight. Darker materials, in particular, absorb more solar radiation. A black leather seat can exceed 70 degrees Celsius in direct sunlight. Metal finishes can become uncomfortable or even painful to the touch. Materials with better solar reflectivity stay cooler and improve the overall passenger experience.
• Energy efficiency and fuel savings: Hot cabins require more powerful air conditioning. This leads to:
  • Higher fuel consumption in internal combustion vehicles.
  • Reduced driving range in electric vehicles.
  • Increased compressor workload

In electric vehicles in particular, cabin cooling can significantly reduce battery range during summer driving. Using materials with lower heat absorption helps:

• Reduces the need for cooling.
• It increases energy efficiency.
• It extends the range of electric vehicles.

• Skin cracking
• Color fading
• Plastic deformation
• Adhesive failure
• Surface brittleness

Repeated heating and cooling cycles also cause thermal stress. Manufacturers test the heating behavior of materials to ensure they retain their appearance, mechanical strength, texture, and safety performance characteristics throughout years of use.

• Safety considerations: High surface temperatures can pose safety risks. For example, they can cause burns from overheated seatbelt buckles or steering wheels, lead to dangerously high temperatures for children or pets, or reduce driver comfort and concentration. Some materials can also release volatile organic compounds (VOCs) more quickly at high temperatures, affecting cabin air quality.
• Electric vehicle thermal management: Modern electric vehicles rely heavily on efficient thermal design. Unlike gasoline vehicles, electric vehicles cannot easily utilize abundant engine waste heat or tolerate excessive HVAC energy losses. Therefore,
  • Cabinet thermal loads are more important.
  • Heat-reflective materials are becoming more valuable.
  • Solar energy management improves overall efficiency.

Therefore, car manufacturers are increasingly seeking new technologies to provide infrared reflective pigments, cool-touch coatings, and advanced composite materials for enhanced protection.

• Climate and sustainability goals: Reducing cabin temperature contributes to sustainability. Lower cooling requirements mean:
  • Lower fuel consumption
  • Lower carbon dioxide emissions
  • Improved battery efficiency
  • Less environmental impact

This supports broader automotive goals related to energy efficiency, emission reduction, and sustainable mobility.

• The perception of premium vehicle quality: The Mercedes-Benz Group and other luxury brands place great emphasis on thermal comfort, as it influences perceived quality. A cooler seat surface, armrest, or steering wheel creates a more refined customer experience.

In conclusion, heating behavior is important because it affects almost every aspect of vehicle performance and user experience:

• Comfort: Cooler cabin surfaces.
• Efficiency: Lower air conditioning energy consumption.
• Durability: Longer material lifespan.
• Safety: Lower risk of burns.
• Electric vehicle performance: Improved driving range.
• Sustainability: Lower emissions

As vehicles become more advanced and electrified, thermal materials engineering is becoming an increasingly important part of automotive design.

For many years, our organization, with its competent and experienced team, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the Daimler PAPP PWT 7333 standard.