Modern car doors are complex assemblies made from a variety of materials, but the outer skin and primary structural frame are typically steel or aluminum. The choice depends on the vehicle's price point, performance goals, and desired fuel efficiency. Lower-priced models almost exclusively use steel for its low cost and high strength, while luxury and performance vehicles increasingly use aluminum or even carbon fiber to reduce weight.
Beyond the metal shell, a car door contains several other key components:
- Inner Frame: This is the door's skeleton, usually made from high-strength steel, which provides crucial protection in a side-impact collision.
- Window Glass: This is tempered safety glass, designed to shatter into small, dull pieces instead of sharp shards upon impact.
- Window Regulator: The mechanism that raises and lowers the glass, often constructed from steel or durable plastics.
- Door Panel/Trim: The interior part you see and touch is typically made from various polymers (plastics), vinyl, and often reinforced with fiberboard. Higher-end models may incorporate genuine wood, aluminum trim, or leather.
- Insulation and Seals: Acoustic foam and butyl rubber sheets are applied to the inner metal skin to dampen road noise, while rubber seals around the door perimeter keep out water and wind.
The industry's push for better fuel economy is driving a shift toward lighter materials. Aluminum, which is about one-third the density of steel, is becoming more common even in mainstream vehicles. Some exotic sports cars use carbon fiber reinforced polymer (CFRP) for doors to achieve extreme weight reduction. The following table illustrates the common usage of these primary materials across vehicle segments.
| Vehicle Segment | Primary Door Skin Material | Common Inner Frame Material | Key Characteristics |
|---|
| Economy / Mainstream | Steel | High-Strength Steel | Cost-effective, highly durable, repairable |
| Luxury / Performance | Aluminum | High-Strength Steel / Aluminum | Lighter weight, improves handling and MPG |
| Full-Size Trucks/SUVs | Steel or Aluminum Mix | Ultra-High-Strength Steel | Maximizes strength and crash protection |
| Exotic Sports Cars | Carbon Fiber | Carbon Fiber or Aluminum | Extreme weight savings for peak performance |
