The working conditions of auto foundry workshops feature splashes of molten metal, continuous high-temperature thermal radiation and convective heat waves. The protective capacity of high-temperature fire-resistant suits worn by workers originates from the fabric and auxiliary material system. Foundry environments differ from ordinary welding scenarios; workers face impacts from higher-temperature molten metal droplets and prolonged exposure to radiant heat. The suit materials must deliver excellent flame retardancy, heat insulation and molten splash resistance, while maintaining mechanical strength, wear resistance, flexibility and wearing comfort. A complete protective suit consists of outer shell fabric, thermal insulation lining, flame-retardant sewing threads, protective accessories and composite membrane layers. The selection of each material, composite manufacturing process and layered matching directly determine the protective efficiency, service life and wearing experience of the suit under high-temperature conditions. The design of the material system requires comprehensive evaluation based on thermal radiation intensity, type of molten metal, ambient temperature and working duration at auto foundry stations to strike a balance between protective performance, material weight and flexibility.

　　The outer shell fabric serves as the first barrier against high heat and molten slag splashes and is the core material of the whole protective equipment. The outer material must satisfy multiple indicators simultaneously: flame retardancy, resistance to molten metal splash, high-temperature tolerance, wear resistance and tear resistance. Commonly used high-temperature flame-retardant woven fabrics include aramid fabrics, pre-oxidized fiber fabrics and aramid blended fabrics. Aramid fibers possess a stable aromatic polymer structure. They do not melt and drip under high heat; upon heating, they merely carbonize without molten droplets that may burn skin. Their breaking strength remains relatively high under elevated temperatures, and they deliver good wear and tear resistance, suitable for the rough operating environment in foundry workshops. Pure aramid fabric provides reliable protection but feels stiff, causing fatigue after long hours of wear. For this reason, blended modification schemes are widely adopted in the industry. Aramid is blended with flame-retardant viscose and high-temperature functional fibers to retain high-temperature flame resistance while improving fabric softness and lowering overall weight.

　　Pre-oxidized fiber fabric is another optional outer-layer material for foundry fire suits. Treated through high-temperature pre-oxidation, this material has a high limiting oxygen index. It will not burn or melt and drip when exposed to open flame, and exhibits outstanding resistance to instantaneous high-temperature shock with stable performance against molten metal splash. Compared with aramid materials, pre-oxidized fiber woven fabrics form dense carbonized layers and have lower thermal conductivity, which can block part of radiant heat from transferring inward. Its drawback lies in relatively weak mechanical properties; wear resistance and tear resistance are inferior to aramid. Hence, it is rarely used alone as outer fabric. It is generally blended with aramid fibers to combine splash protection and mechanical durability. During material selection tests, outer woven fabrics undergo molten metal splash trials using molten metal actually applied in foundry workshops. Inspect fabric damage, back-side temperature rise and droplet generation to verify material reliability under real working conditions.

　　Thermal insulation lining material blocks radiant heat and conductive heat, acting as the core interlayer for thermal protection. Although the outer fabric stops slag splashes, radiant heat can still penetrate the surface. The lining material slows heat transfer toward human skin and extends safe working duration. Insulation linings mostly adopt high-temperature fiber felt and needle-punched composite materials, mainly made from aramid fiber batting and pre-oxidized fiber batting. Numerous static air pockets form between fibers. Air itself has low thermal conductivity, and large quantities of closed micropores effectively block heat conduction. The thickness of lining material affects insulation directly; thicker material brings better heat resistance yet adds suit weight and reduces limb mobility. Workers in auto foundry workshops frequently bend, lift arms and turn their bodies. Overly thick and bulky lining material restricts movement. Therefore, fiber felt density must be controlled to form a stable thermal barrier within limited thickness.

　　Lining materials also require stable resistance to heat and humidity. Temperatures inside foundry workshops remain high, and workers sweat heavily. Water vapor penetrates into the interlayer. If insulation performance drops sharply upon wetting, protective capacity declines. Poor-quality thermal fiber materials suffer structural collapse of fibers when wet, with disappearing pores and obvious loss of insulation performance. High-quality high-temperature fiber felt is modified on the surface with certain water repellency. Sweat does not soak into fiber bodies in large quantities, keeping microporous structures stable. Meanwhile, lining materials must maintain good air permeability to allow water vapor to escape outward, reducing accumulated heat and sweat inside the suit and alleviating stuffiness during high-temperature wear. Apart from static insulation tests, material inspection includes hydrothermal aging tests simulating long-term high-temperature and high-humidity environments to evaluate the attenuation of insulation performance.

　　Barrier films and functional composite layers are easily overlooked components in the suit material system, placed between outer fabric and thermal lining. In foundry environments, when molten metal splashes impact fabric, tiny hot particles and high-temperature flue gas may penetrate gaps in the outer layer. High-temperature polymer barrier films resist combustion, block hot fine particles and hot smoke from penetrating inward, without preventing water vapor discharge outward. Ordinary plastic films cannot be used; conventional polymer films melt and shrink under high heat and lose protective effects. Such functional films adopt high-temperature polyimide films or flame-retardant composite films. They are bonded to woven fabrics by hot pressing. The composite process is critical. Adhesives must also be high-temperature flame-retardant adhesives. Common adhesives melt and fail upon heating and cause delamination between layers. Delamination damages the overall protective structure and greatly shortens service life.

　　Auxiliary materials including sewing threads, zippers and hook-and-loop fasteners often become weak points of protection. Many protective suits pass fabric performance tests yet fail prematurely because auxiliary materials cannot withstand high heat, leading to loss of protection. Sewing threads must be aramid flame-retardant threads. Ordinary cotton or polyester threads quickly melt and break under high temperature. Broken stitches create openings in the suit, allowing molten slag to intrude through seams. Zippers should be high-temperature resin zippers or metal zippers, and zipper tapes must be woven from flame-retardant aramid fabric. Metal zippers conduct heat rapidly and may transfer heat under high-temperature conditions and burn skin upon contact. Therefore, zipper surfaces require an additional thermal protective flap. Base fabric and hook surfaces of hook-and-loop fasteners must also be woven from high-temperature flame-retardant fibers. Ordinary nylon hook-and-loop fasteners soften and deform under heat and lose adhesion, leaving unclosed openings on protective suits and forming protection gaps. All auxiliary materials undergo high-temperature aging and flame retardancy tests together with main fabrics, ensuring their high-temperature resistance matches or exceeds that of primary fabrics.

　　Post-finishing processes of materials directly change the final protective performance of woven fabrics. Finishing of high-temperature flame-retardant protective suit fabrics cannot rely on conventional dipped flame-retardant coatings. After continuous exposure to radiant heat and repeated friction, flame-retardant coatings on ordinary coated fabrics peel off easily, causing rapid degradation of protective performance, making them unsuitable for long-term use in foundry workshops. Foundry protective suits prefer inherently flame-retardant fibers. The polymer structure of fiber itself has built-in flame resistance, and protective performance will not fade through friction or washing. Some fabrics are equipped with additional anti-splash coatings. When impacted by molten metal, these coatings rapidly form dense carbonized layers to block droplets from penetrating fabric. Post-finishing also includes anti-static treatment. Foundry workshops contain abundant dust, and static accumulation may introduce risks. Fabrics modified for anti-static properties suppress static charge accumulation under dry and high-temperature conditions. Coating thickness must be controlled during post-finishing; excessively thick coatings stiffen fabrics and reduce mobility.

　　A material’s resistance to aging and washing determines the service life of protective suits. In auto foundry workshops, suits are exposed to dust, metal oxides and oil contaminants and require regular cleaning and maintenance. After repeated washing cycles, some high-temperature fiber materials experience fiber damage, reduced strength and attenuation in heat insulation and flame retardancy. Therefore, material development includes repeated washing cycle tests to detect changes in fabric breaking strength, limiting oxygen index and insulation performance after washing. Inherent high-temperature materials such as aramid and pre-oxidized fibers have better washing stability, with minor performance degradation after repeated cleaning. Besides washing aging, materials must pass thermal aging tests simulating long-term storage and use under high heat to check for fabric embrittlement and powdering. Material aging is a gradual process. Regular inspections help predict declining protective capacity and retire suits once they reach the end of service life.

　　Material selection must balance safety specifications and ergonomics. Pursuing ultra-high temperature resistant materials alone results in thick, stiff fabric that restricts worker movement and reduces operating efficiency. Overemphasis on lightness and softness sacrifices thermal insulation and droplet splash protection. For this reason, layered material design is adopted. Torso and arm areas exposed to high heat and splashes adopt multi-layer composite structures for enhanced protection; joint positions use lightweight, highly flexible high-temperature fabrics to guarantee freedom of movement for arms and waists. In terms of material safety, all woven fabrics, adhesives and auxiliary parts shall not release large volumes of toxic smoke when heated. Foundry workshops are relatively enclosed, and harmful gas released from thermal decomposition of materials endangers worker health. Material testing includes heat release and smoke toxicity tests to control emissions of hazardous substances.

　　In summary, the protective capability of high-temperature flame-resistant suits is realized by the complete multi-layer material system. A single fabric cannot satisfy the complex working conditions of foundry workshops. Outer woven fabric resists molten metal splashes; inner fiber felt blocks heat conduction; barrier films stop high-temperature fine particles and smoke; flame-retardant auxiliary materials maintain protection at seams and openings. Combined with reliable fiber modification and post-finishing technology, they form complete protection. Material selection requires full assessment of working environments and verification through thermal radiation, molten droplet impact, hydrothermal aging and washing durability tests. Proper material matching can defend against molten metal splashes and sustained high-temperature radiant heat inside auto foundry workshops, safeguard worker safety, while preserving fabric flexibility and air permeability, reducing stuffiness and load during long-time wear and meeting demands for extended operation at foundry stations.