A significant number of field cases show that passing UL94 does not guarantee flame-retardant reliability at the system level. In multi-material assemblies, flame-retardant nylon components are often placed adjacent to non-flame-retardant plastics such as TPE or PBT. Volatile combustible gases released by neighboring materials during ignition can alter the local flame environment, reducing the self-extinguishing capability of the nylon component. This type of system-level failure cannot be captured by single-material UL94 testing but represents a high-frequency risk in end-use products. Another common source of failure is long-term aging and service environment. UL94 tests are typically performed on new materials and freshly molded parts. In real service, components are exposed to prolonged thermal aging, electrical stress, and humid conditions. Certain additive-type flame retardants may migrate or hydrolyze under high temperature and humidity, leading to reduced surface flame-retardant concentration. In practice, products that initially pass testing may fail after 85℃/85%RH aging, exhibiting dripping or sustained burning. From a validation standpoint, more engineering teams are supplementing UL94 with tests such as GWIT, GWFI, and glow-wire testing on finished components. At the material selection stage, specifying the actual minimum wall thickness and requesting flame-retardant data at that thickness, rather than relying on the “best-case” thickness in certification reports, has proven effective in reducing end-use failure risk.

In applications such as electrical and electronic devices, industrial control systems, and new energy vehicles, flame-retardant nylon is often considered a default material choice. When a material achieves a UL94 V-0 or V-1 rating during the selection phase, it is commonly assumed that regulatory and safety requirements have been fully satisfied. However, failures such as sustained burning, molten dripping, or secondary ignition are still frequently observed during final product certification, customer audits, or even real service conditions. These failures are rarely caused by a single factor; instead, they result from gaps between standardized material testing and real engineering application. In real engineering scenarios, UL94 testing is conducted on standardized specimens with strictly controlled thickness, orientation, and ignition conditions. Actual molded parts, however, often feature complex geometries including ribs, thin walls, inserts, and multi-directional weld lines. When the minimum wall thickness of a component falls below the thickness used for UL94 certification, the effectiveness of the flame-retardant system changes fundamentally. The protective char layer formed during combustion may no longer develop continuously, leading to rapid burn-through in localized thin sections. This phenomenon is particularly common in relay housings, terminal supports, and connector components. From a material perspective, the UL94 rating of a flame-retardant nylon is not an intrinsic property but the result of interactions between the flame-retardant system, the base polymer, filler content, and processing history. In PA66-based systems, for example, flame retardancy relies heavily on the formation of a dense char layer during combustion. This process is highly sensitive to moisture content, shear heat, and molecular weight distribution. Excessive melt temperature or prolonged residence time during injection molding can partially degrade the flame-retardant additives. As a result, standard UL94 specimens may still pass, while complex molded parts lose stable self-extinguishing behavior.

Processing data indicate that, under identical tooling and processing conditions, PA66 GF40 exhibits a mold wear rate 1.6–1.8 times higher than GF30, particularly in high-flow regions. Additionally, high glass fiber systems demand higher injection pressure and speed, further intensifying abrasive effects. Beyond mechanical abrasion, excessive reinforcement also accelerates thermal fatigue of molds. Reduced thermal uniformity causes larger temperature gradients per molding cycle, increasing micro-crack initiation risks, especially in standard H13 or P20 tool steels. Industrial experience shows that many failures originate not from insufficient material strength, but from over-reliance on high glass fiber content. In one connector application, increasing fiber content from GF35 to GF50 reduced mold life from an expected 800,000 cycles to less than 300,000 cycles, increasing hidden manufacturing costs by over 20%. Ultimately, glass fiber content selection is a balance between structural performance, processing stability, and manufacturing economics rather than a pursuit of maximum reinforcement.