Air-intake manifolds, cooling ducts, battery housings. Glass-filled PA66, PA6, and increasingly PP for cost-down.
Engine-bay components are typically glass-filled polyamide (PA66 or PA6) for the most thermally demanding parts (intake manifolds, valve covers), and glass-filled or talc-filled polypropylene (PP) for less demanding parts (fan shrouds, battery housings, fluid reservoirs). All grades are formulated to meet ISO 16750 thermal cycling and chemical resistance requirements.
Plastic engine components weigh 30–50% less than the aluminium or steel parts they replace, which improves fuel economy and CO₂ emissions. Glass-filled PA66 intake manifolds, for example, save about 1.5 kg per vehicle versus aluminium. Plastic also enables more complex internal geometry (like integrated coolant channels) that would require multi-piece metal assemblies.
Engine-bay polymers are formulated to specific continuous-service temperatures: glass-filled PA66 handles 150–180 °C continuously; PP-based grades top out around 130 °C. Components placed near the exhaust manifold or turbocharger require higher-grade polymers (PPS, PEEK) or stay in metal. Manufacturers map under-hood thermal zones during platform development to assign the right material to each part.
EV battery module housings increasingly use flame-retardant polypropylene (FR-PP) — a halogen-free formulation that meets UL94 V-0 and provides high voltage tracking resistance for bus-bar proximity. Glass-filled PA is also used for some structural components. The shift from aluminium to plastic battery housings can save 30–40% on weight at module level, an important factor in EV range.