OEM specified Plastic Tank-Aluminum Core Construction Tanks are made from Virgin Grade Engineered plastic resins, which are 'Glass Filled' for added Strength & Durability Gaskets are made from Special Grade 'EPDM' rubber to withstand extreme temperatures of up to -120 Degrees F Fins (Heart of Radiator) - High Performance 'Multi-Louvered Design' 100% leak tested before leaving factory at 150% of operating pressure