What Car Bodies Are Made Of

Most modern car bodies are primarily made of steel, increasingly mixed with aluminum, and complemented by plastics and composites; some niche models use stainless steel or carbon fiber. In detail, automakers combine materials to balance safety, weight, cost, manufacturability, durability, and sustainability, with the “body-in-white” structure often steel-dominant and outer panels, closures, and crash parts selectively in aluminum or polymers.

The Modern Body-in-White: Core Materials

Automakers typically refer to the structural shell before paint and trim as the body-in-white (BIW). This skeleton includes the roof, pillars, floor, and rails that protect occupants and define stiffness. Outer “skin” panels—hoods, fenders, doors, bumpers—may use different materials optimized for dent resistance, corrosion performance, styling, and pedestrian safety regulations.

Steel (mild, high-strength, and ultra-high-strength)

Steel remains the backbone of most BIWs due to its crash performance, cost efficiency, and well-understood manufacturing. Automakers deploy a mix of mild steel for easy forming, high-strength low-alloy (HSLA) for stiffness with reasonable formability, and ultra-high-strength steels (UHSS), including press-hardened steel (hot-stamped boron steel), for critical crash zones like pillars, sills, and door rings. Third-generation AHSS grades continue to spread, offering better strength-ductility trade-offs to reduce weight without sacrificing safety. Galvanized and galvannealed coatings plus e-coat primers provide corrosion protection.

Aluminum (sheet, castings, and extrusions)

Aluminum is favored where weight savings matter—hoods, fenders, doors, liftgates, crash beams, battery enclosures, and increasingly structural parts. Sheet aluminum reduces mass and improves fuel economy or EV range, while large die castings (“gigacastings”) can replace dozens of welded pieces in front or rear body structures, cutting complexity. Aluminum requires specialized joining (rivets, self-piercing rivets, adhesives) and careful isolation from steel to prevent galvanic corrosion. Premium SUVs and trucks, and models like Ford’s F-150, use extensive aluminum on body panels.

Magnesium (limited use)

Magnesium is the lightest structural metal used in vehicles but is costlier and more challenging to form and protect. It appears in limited structural brackets, seat frames, and occasionally inner panels or instrument panel supports, less often in exterior BIW parts.

Plastics and elastomers

Thermoplastics such as polypropylene (PP), ABS, PC/ABS, and thermoplastic olefins (TPO) are common for bumper covers, grilles, rocker claddings, wheel-arch liners, and underbody shields. They enable complex shapes, integrate mounts, and improve pedestrian impact compliance. Paintable grades deliver exterior finish; unpainted textured plastics resist chipping in high-debris zones. Energy absorbers behind bumpers are often expanded polypropylene (EPP) or similar foams.

Fiber-reinforced composites

Glass fiber-reinforced plastics (GFRP) and carbon fiber-reinforced polymer (CFRP) offer excellent stiffness-to-weight ratios. GFRP is used for non-structural body panels on certain sports cars and trucks, while CFRP appears in performance and premium EVs for roofs, tubs, or reinforcements. BMW’s i3 popularized a CFRP passenger cell in volume production. Composites can reduce weight dramatically but are expensive and harder to repair and recycle compared to metals; thermoplastic composites are emerging to improve recyclability.

Stainless steel and other niche materials

Stainless steel is rare because it is harder to stamp, heavier than aluminum, and costlier than painted mild steel. An exception is the Tesla Cybertruck, which uses thick cold-rolled stainless for exterior body panels in an exoskeleton approach, trading formability for dent resistance and corrosion durability. Titanium and advanced alloys are extremely rare in body structures due to cost.

Typical Material Breakdown in a Mass-Market Vehicle Body

While exact mixes vary by model and segment, the following ranges describe how materials commonly appear in contemporary body structures and exterior panels. Percentages reflect the body and closures rather than the entire vehicle.

• Steel (mild, HSS, AHSS/UHSS): roughly 50–75% of BIW mass in most mainstream vehicles
• Aluminum (sheet, castings, extrusions): roughly 10–35%, higher on lightweight-focused models and trucks/SUVs
• Plastics and foams (bumpers, shields, trims, energy absorbers): common by part count; modest by mass
• Composites (GFRP/CFRP): minimal to moderate, often limited to specific panels or reinforcements
• Magnesium and other alloys: small fractions in selective brackets or panel inners
• Stainless steel: niche applications on select models

These ranges underscore a multimaterial strategy: steel dominates core structure for safety and cost, aluminum trims weight, and plastics/composites tailor surfaces and impact performance.

Why Automakers Mix Materials

Material choice is a balancing act. The following considerations usually determine the blend for a specific model and market.

1. Safety and stiffness: High- and ultra-high-strength steels create strong safety cages and precise handling.
2. Weight and efficiency: Aluminum and composites reduce mass, boosting fuel economy or EV range.
3. Cost and manufacturability: Steel stamping and spot welding are fast and economical at scale.
4. Corrosion and durability: Galvanized steels, aluminum, and coatings improve longevity.
5. Repairability and insurance: Metals are widely repairable; composites and adhesives can complicate repairs.
6. Design and surface quality: Aluminum and plastics enable sharp creases or complex forms; steel offers excellent panel finish.
7. Sustainability: High recycling rates for steel and aluminum help lifecycle CO2; composite recycling is improving but lagging.

The optimal mix varies by vehicle purpose: city cars focus on affordability, luxury SUVs on refinement and weight savings, and performance EVs on stiffness-to-weight and aero.

How the Pieces Come Together

Joining and finishing methods must match the material set to ensure crash integrity, quietness, and durability.

• Resistance spot welding and laser welding: Fast, economical for steel-intensive BIWs.
• MIG/TIG welding: Used for aluminum structures and repairs; more heat-input sensitive.
• Self-piercing rivets (SPR), flow-drill screws, and clinching: Mechanical fasteners that join dissimilar sheets without pre-drilling.
• Structural adhesives: Add stiffness, improve NVH, and seal joints; widely used alongside welds/rivets.
• Surface protection: Zinc-coated steels, e-coat dip, seam sealers, underbody coatings, and multi-layer paints mitigate corrosion and chips.

Success in mixed-material bodies depends on compatible joining stacks, controlled heat input, and isolation to prevent galvanic corrosion between steel and aluminum.

Trends to Watch (2024–2025)

Automakers are accelerating multimaterial strategies. Large aluminum die castings (“gigacastings”) simplify front and rear body sections on some EVs; structural battery packs integrate the floor into the body to boost rigidity. Third-generation AHSS continues to spread in crash-critical rings. Stainless exoskeleton experiments, while rare, highlight durability trade-offs. Industry-wide, recycled-content aluminum and low-CO2 steel (including electric-arc furnace and direct-reduced iron pathways) are gaining attention to meet sustainability targets, while thermoplastic composites aim to improve circularity.

Notable Examples

Several recent models illustrate how different material strategies serve different goals.

• Ford F-150 (current generation): Aluminum outer body panels on a steel frame to reduce mass while maintaining capability.
• Tesla Model Y: Mixed-material shell with large aluminum castings for rear (and in some variants front) structures, plus steel-intensive safety cell.
• Tesla Cybertruck: Thick stainless-steel exterior panels as part of an exoskeleton-influenced design.
• BMW i3 (earlier 2010s–2020s): CFRP passenger cell on an aluminum chassis, showcasing lightweight composite structures.
• Chevrolet Corvette: Aluminum-intensive structure with composite body panels for weight and performance.
• Range Rover: Predominantly aluminum BIW for large luxury SUV weight reduction.

These cases show there is no single recipe; each model’s mission drives the material palette and manufacturing approach.

Summary

Car bodies today are usually steel-based structures enhanced with aluminum, plastics, and composites where they add specific advantages. Ultra-high-strength steels deliver safety and stiffness; aluminum trims weight and enables megacastings; polymers tailor exterior form and impact behavior; composites appear where performance justifies cost; and stainless steel remains a niche experiment. The result is a carefully engineered multimaterial shell tuned for safety, efficiency, cost, durability, and sustainability.

When did cars stop being made of metal?

Cars never completely stopped being made of metal; rather, metal became a material alongside plastic, aluminum, and other materials, rather than the sole primary component. While the industry shifted toward mass production of steel-bodied cars in the early 20th century, the use of other materials like plastic increased significantly from the mid-20th century onwards to reduce weight, improve fuel efficiency, and meet emissions standards.
 
History of Metal in Cars

• Early 20th Century: The introduction of the first all-steel-bodied automobile in 1914 by Dodge marked a major shift, with steel bodies becoming the standard by the late 1930s. 
• Mid-20th Century: Steel continued to be the primary material for car chassis and bodies through the early 1970s and beyond. 
• Late 20th Century: Despite the prevalence of steel, there was also a shift towards using more aluminum for bodies to improve fuel economy. 
• Modern Cars: Today, cars are made from a combination of materials, including steel, plastic, aluminum, rubber, and glass. 

Reasons for Material Diversification 

• Weight Reduction: The use of plastic and aluminum in vehicles helps to reduce overall weight.
• Fuel Efficiency: Lighter vehicles require less fuel, improving fuel economy.
• Emissions Standards: Reducing fuel consumption also leads to lower emissions, helping manufacturers meet stricter environmental regulations.

What material are car bodies made from?

Steel is one of the most common materials in car manufacturing because it is strong, inexpensive, accessible, and easy to handle and transform into auto parts, such as chassis, wheels, brakes, or engines. Aluminum is a lightweight but strong metal resistant to corrosion.

Why are car bodies not made of plastic?

There are a few reasons why cars don’t have more plastic body panels. The first is that plastic is not as strong as metal, so it can’t be used in areas that need to be strong, like the frame of the car. Additionally, plastic is more expensive to produce than metal, so it would be more expensive for the consumer.

What were the bodies of cars in 2025 made of?

The study finds that every leading automaker will have numerous aluminum body and closure programs by 2025. As the material mix for body and closure parts continues to change in the years to come, use of aluminum sheet for vehicle bodies will increase to 4 billion pounds by 2025, from 200 million pounds in 2012.