Flammability in automotive adhesives

Flammability in automotive adhesives


In the complex landscape of the automotive industry, ensuring adhesive and label materials conform to stringent regulations is paramount. While the number of flammability testing standards can seem daunting, understanding the ins and outs of these tests is critical for compliance. We are here to help explain these tests' complexities, ensuring manufacturers can confidently select the right adhesive solutions.

At Avery Dennison we are constantly innovating our adhesive materials that not only meet manufacturers' expectations but also strengthens production efficiencies. Our wide array of solutions, including those suitable for EV batteries, have been expertly developed, tailored, and externally tested (in line with UL 94 and FMVSS 302 flammability tests) to cater to diverse automotive applications. At the heart of these tests is a critical question: How do these materials behave when exposed to flames?


Flammability in automotive adhesives


Horizontal vs. vertical burn testing

Flammability characteristics vary significantly based on the orientation in which materials are tested. Horizontal testing generally has less stringent requirements compared to its vertical counterpart. The chosen test method often hinges on the specific rating the material needs to achieve, typically prescribed by the customer or Original Equipment Manufacturer (OEM).

The automotive industry commonly adopts the American FMVSS 302 (Federal Motor Vehicle Safety Standard) as its flammability benchmark, with ISO 3795 being its global equivalent. However, with the surge of electric vehicles, the UL® 94 test method, devised to classify the burning behavior of plastics in electric devices, is gaining traction. Here's a closer look at both:


Underwriters Laboratories Incorporated Safety Standard UL® 94

This standard specifies several variations to the method based on the types of materials to be tested, their thickness, rigidity, and burning characteristics. Some variations align with other testing standards and ratings.

UL® 94 HB (horizontal burn): Tailored for materials like untreated polyolefins, this test is conducted in a horizontal orientation, and results from this method yield a burn rate for a material—in other words, how long it will take for a material to burn. To be classified as HB, a material shouldn't exceed a burn rate of 40 mm per minute over a 75 mm span for specimens 3 to 13 mm thick—or a burn rate less than 75 mm over a 75 mm span if less than 3 mm thick. Furthermore, all specimens must cease to burn before hitting the 100 mm mark.

UL® 94 V (vertical burn): This method evaluates solid materials' (with a maximum thickness of 12.7 mm) resilience against flame-induced shrinkage or distortion. Five test specimens for each material, 127 mm long by 12.7 mm wide, are supported vertically rather than horizontally. A flame is applied to the bottom of each specimen, held for 10 seconds, and then removed until it extinguishes. After ten seconds, the flame is reapplied, and the length of the burn or afterglow time is recorded. Any specimen that drips and ignites a wad of cotton placed beneath the specimen is also recorded. A rating of UL® 94 V-0 is the best achievable rating, and any material with this score is considered flame retardant. Labeling materials less than 0.38 mm thick are unlikely to meet the "V" rating requirements. 

UL® 94 VTM (very thin materials): Catering specifically to ultra-thin materials susceptible to shrinkage, distortion, or consumption up to the holding clamp, the method starts by ensuring that test specimens are 200 mm by 50 mm. On each specimen, a mark is positioned 125 mm from the bottom, spanning its width. These specimens are then tightly wrapped around a 12.7 mm mandrel and secured using tape or wire just above the 12 5mm line. Once the mandrel is removed, the specimen is clamped vertically and tested following the procedures outlined in the "V" protocol. This approach is specially tailored for label materials thinner than 0.254 mm and designed with flame-retardant features.


Flammability in automotive adhesives


FMVSS 302 (ISO 3795): Fire retardancy in the automotive industry 

The Federal Motor Vehicle Safety Standard 302, or FMVSS 302, is a flammability test tailored specifically for the automotive sector. This standard becomes particularly significant for materials utilized within vehicles' passenger and engine compartments. Recognized and endorsed by most OEMs, it often proves to be a more compatible testing protocol for our solutions compared to the UL 94®.

The testing procedure of FMVSS 302 is similar to UL® 94 HB. In the test, a sample is clamped within a horizontal "U" fixture. One end of the sample is then subjected to an open flame. After exposure, the flame is withdrawn, and the burn rate of the sample is examined. This burn rate is calculated and then expressed as the distance burned over time. For a material to earn the classification of being "self-extinguishing," it should stop burning in less than 60 seconds, with the flame not having traveled more than 100 mm. This test can be performed with the label material on its own or in combination with the substrate it is applied to. It is important to note that when labels are combined with substrates showcasing slow-burning properties, they might still meet the prescribed criteria, even if the labels themselves are of a standard variety.


Steering towards the optimal solution

While UL® 94 champions individual components' flame retardancy, it could inflate design, development, and production expenses. It's essential to remember that in automotive applications, a label invariably bonds with a component, be it in seat heating or battery pack designs. FMVSS 302 mandates testing the topmost 13 mm of any component. Avery Dennison's expertise can guide you to materials that not only pass the FMVSS 302 but also the more rigorous UL® 94.



Flameproof: Resistant to damage or burning when in contact with a flame. 

Inflammable (similar): Not capable of supporting combustion or being ignited.

Flame resistant: Resistant to ignition by a flame source for a limited time. Flame-resistant items are not flameproof. Wet wood is an example of a flame-resistant material. It will not support a flame or burn until dried.

Flame retardant: Made or treated to resist burning for a certain period of time. Flame retardant materials are not flameproof. Children’s sleepwear and flame-retardant plastic are examples of flame-retardant materials.

Flammability: The ability to support combustion.

Flammable: Capable of being easily ignited and of burning quickly.

Self-Extinguishing: Material that burns in the presence of a flame or intense heat source but stops burning after a period of time when that source is removed. 


Learn more about Avery Dennison's solutions that meet flammability requirements.