what are car doors made of

[JamesonRose]

Modern car doors are complex assemblies made from a variety of materials, but the most common are steel, aluminum, and plastic composites. The choice depends on the vehicle's price point, desired weight savings, and safety goals. The outer skin is typically steel or aluminum for durability and formability, while the internal structure, including the side impact beam, is often high-strength steel. Interior panels are primarily made from plastic composites like polypropylene for cost-effectiveness and design flexibility.

The primary function of a car door is to provide safe entry and exit while protecting occupants in a side-impact collision. This is why the internal structure is so critical. A robust door intrusion beam, mandated by U.S. safety standards like FMVSS 214, is integrated into the door's frame to absorb and redirect crash energy away from the passenger cabin.

Here’s a breakdown of common materials and their applications:

Component	Common Materials	Key Reasons for Use
Outer Panel (Skin)	Mild Steel, Aluminum	Durability, ease of shaping, corrosion resistance (with coatings)
Inner Frame/Structure	High-Strength Steel (HSS), Ultra-High-Strength Steel (UHSS)	Maximum strength for side-impact protection, rigidity
Side Impact Beam	Ultra-High-Strength Steel (UHSS), Boron Steel	Extreme strength-to-weight ratio to resist intrusion in a crash
Inner Trim Panel	Polypropylene, ABS Plastic	Lightweight, low cost, allows for complex designs (armrests, speaker grilles)
Window Mechanism	Steel, Aluminum	Strength to reliably raise and lower the heavy glass window
Weather Seals	EPDM Rubber, Thermoplastic Elastomers (TPE)	Flexibility, excellent waterproofing and sound insulation
Window Glass	Tempered Glass, Laminated Glass	Safety (shatters into small, dull pieces) and security

Higher-end vehicles, especially sports cars and luxury sedans, increasingly use aluminum or even carbon fiber for the outer skin and structure to reduce weight, which improves fuel efficiency and handling. The trend is toward multi-material designs, using the right material in the right place to optimize safety, cost, and performance.

[NicoleDella]

From a safety and repair standpoint, it's all about the steel inside. The visible metal is just the skin. What matters is the ultra-high-strength steel beam hidden inside the door. That's what protects you in a T-bone accident. When I see a car after a side impact, I'm looking for how that beam held up. For the interior, it's mostly various plastics—tough, flexible, and cheap to replace. It’s a smart mix of heavy-duty stuff where you need it and lighter materials everywhere else.

[McAubrey]

I always notice the sound a door makes when it closes. A solid thunk usually means a heavier steel construction, which feels more premium. My friend’s economy car has doors that sound tinny and light, probably using thinner steel or more aluminum to save weight. The interior door handle and armrest materials matter too—some are hard, scratchy plastic, while others are soft-touch. You can tell a lot about a car's build quality just by interacting with its doors before you even drive it.

[LeRuby]

As a parent, my focus is on durability and safety. I need doors that can withstand constant slamming open and shut by kids. The plastic panels are great for that—they wipe clean and don't dent. But more importantly, I researched and made sure our SUV had strong side-impact crash ratings. Knowing there's a solid steel beam inside the door gives me peace of mind when I'm driving my family around town. The materials aren't just about looks; they're a crucial part of the safety cage.