What Are the Plastic Parts Under a Car?

The plastic parts under a car include engine splash shields (undertrays), belly pans, wheel well liners, aerodynamic underbody panels, bumper lower covers/air dams, rocker covers/side skirts, fuel or line shields, mud flaps, and various clips and fasteners. Together, these components control airflow, reduce noise, protect vital systems from water and debris, and improve efficiency—functions that have grown more important with modern fuel economy standards and the rise of EVs.

Why Automakers Put Plastic Underneath

Over the last decade, underbody plastic has expanded from simple splash guards to full-length aerodynamic paneling. These parts help direct cooling air, minimize drag and lift, dampen road noise, and keep corrosive spray away from the engine bay, wiring, lines, and body structure. On electric vehicles, large, smooth panels can meaningfully increase driving range by improving aerodynamics.

Common Plastic Parts Under a Car

The following items are the most frequently found plastic or composite components beneath passenger cars, crossovers, and many trucks. The list explains what each part does and where it’s typically located.

• Engine splash shield/undertray (belly pan): A broad panel under the engine that deflects water and debris, smooths airflow, and can guide cooling air through the radiator.
• Transmission/transfer case cover: Similar to the engine undertray, but positioned under the gearbox or transfer case to protect and streamline.
• Front bumper lower cover, air dam, or chin spoiler: A low-hanging plastic piece that reduces front-end lift and channels air under or around the car.
• Aerodynamic underbody panels (mid-floor covers): Flat panels along the floor that reduce turbulence and drag; widespread on modern vehicles, especially hybrids and EVs.
• Rear diffuser panels/strakes (plastic versions): Shaped pieces at the rear underside that manage wake airflow and can reduce drag and noise.
• Wheel well liners (fender liners): Plastic or felt-like panels inside the wheel arches that block road spray, stones, and salt; they also reduce noise.
• Rocker covers/side skirts: Exterior trim along the sides that can also shield pinch welds and lower body areas from debris.
• Mud flaps/splash guards: Panels behind wheels that minimize spray and gravel impacts on the body and following traffic.
• Fuel tank, brake line, and EV high-voltage line shields: Plastic or composite covers that protect hoses and cables from impacts and abrasion.
• Cable conduit covers and junction box covers: Smaller plastic shields that protect wiring and connectors under the floor.
• Composite skid plates (on some SUVs/crossovers): Lighter-duty “skid” protectors made of reinforced plastic; heavy-duty versions are usually metal.
• Fasteners, push clips, and splash shield retainers: Plastic “Christmas tree” clips and rivets that secure panels; they often fail first after impacts.

Together, these pieces create a protective and aerodynamic shell. While layouts vary by brand and model, most modern vehicles use a combination of these components.

What These Parts Do

Beyond simple protection, underbody plastics serve multiple roles that influence comfort, efficiency, and durability. The following points summarize their main functions.

• Aerodynamics and efficiency: Smoother airflow under the car reduces drag, improving fuel economy or EV range.
• Cooling management: Directs air through radiators and around hot components to stabilize temperatures.
• Noise, vibration, and harshness (NVH): Panels and liners dampen road roar and gravel ping inside the cabin.
• Corrosion and damage protection: Shields deter water, salt, and debris from attacking metal and mechanical parts.
• Safety and compliance: Certain covers help meet pedestrian protection and underbody impact standards.

Because these functions interact—airflow affects both cooling and efficiency—the absence or damage of a single panel can have a noticeable effect on the driving experience and operating costs.

Materials and Heat Considerations

Undercar plastics must balance durability, weight, and cost. The materials below are typical and help explain why some parts feel flexible while others are rigid or felt-like.

• Polypropylene (PP) and high-density polyethylene (HDPE): Common for splash shields and aero panels; light, relatively tough, and affordable.
• ABS and fiber-reinforced plastics: Used where added stiffness is required, including some diffusers and skid-like covers.
• Non-woven PET “felt” liners: Used in wheel wells to reduce noise and trap fine debris.
• Composites with heat shields or insulation: Employed near exhaust paths; plastic is kept at a safe distance or backed by reflective heat barriers.
• Metal nearby high heat: True heat shields are usually aluminum or stainless steel; plastic is not used directly next to hot exhaust components.

In short, plastics are placed where temperatures remain within safe limits, while metals or insulated composites handle high-heat zones.

EVs and Hybrids: What’s Different

Electric and hybrid vehicles lean heavily on underbody design for efficiency and protection. Their layouts bring a few distinctions worth noting.

• Large, continuous aero panels: Broad composite or plastic sheets cover much of the floor to maximize range and reduce wind noise.
• Battery pack protection: The pack enclosure is typically metal, but external covers or deflectors around it may be composite to smooth airflow and guard against debris.
• High-voltage cable covers: Additional plastic conduits and shields route and protect orange HV lines.

While the battery case itself is usually aluminum or steel, the surrounding underbody plastics are crucial for range, thermal management, and debris protection.

Signs a Plastic Underbody Part Needs Attention

Underbody plastics often take the brunt of speed bumps, parking curbs, and road debris. Watch for these symptoms to catch issues early.

• Rattling or flapping at speed: Broken tabs or missing clips can let panels vibrate or drag.
• Visible sagging or scraping: A dropped undertray can contact the road or tires.
• New wind noise or decreased efficiency: Missing aero panels can raise drag and cabin noise; EVs may show slight range loss.
• Overheating complaints: On some models, missing or misrouted panels disrupt cooling airflow.
• Wet, dirty engine bay: A damaged splash shield may let water and grime infiltrate sensitive areas.

Prompt inspection can prevent a minor fastener failure from becoming a torn panel or roadside hazard.

Repair, Replacement, and Costs

Fixes range from simple clip replacements to full panel swaps. Many owners can handle basic repairs; others are best left to a shop.

• Clips and fasteners: Often $5–$25 for assortments; replacing missing clips is a quick DIY.
• Engine splash shields/undertrays: Aftermarket $40–$200; OEM typically $100–$400+. Labor is usually 0.3–1.0 hours.
• Wheel well liners: $50–$250 each, model-dependent; straightforward to replace with basic tools.
• Aero panels and diffusers: $75–$500+ depending on size and material; ensure correct fit to maintain airflow.
• Dealer alignment and torque: For large panels, correct torque and sequence help prevent vibration and warping.

Costs vary widely by brand and trim (luxury and EV models trend higher). If a panel is torn near mounting points, replacement is often more reliable than patching.

Care and Maintenance Tips

Simple routines can extend the life of underbody plastics and preserve efficiency and comfort.

• Inspect after impacts: Check for dangling panels or missing clips after bottoming out or striking debris.
• Rinse road salt and mud: Seasonal washdowns help prevent corrosion of mounting points and reduce abrasive wear.
• Use proper fasteners: Replace with OEM-style clips; mismatched hardware can crack panels or fall out.
• Avoid jacking on panels: Always use approved lift points to prevent cracking undertrays or side skirts.
• Mind heat zones: If a panel near the exhaust is damaged, verify heat shielding before reinstalling.

Regular checks—especially before long trips—can prevent noise, damage, and unexpected efficiency losses.

Bottom Line

The plastic parts under your car are not cosmetic extras—they are engineered components that shape airflow, quiet the cabin, and shield critical systems. Keeping them intact maintains the vehicle’s efficiency, cooling, and long-term durability, and on EVs, helps protect range. If you hear new underbody noises or see something hanging, a quick inspection and low-cost fastener replacement can save a larger repair later.

Summary

Underbody plastics include engine splash shields, belly pans, wheel well liners, aero panels, bumper lower covers, side skirts, line shields, mud flaps, and their clips. Built from PP, HDPE, ABS, and composites (with metal near hot zones), they reduce drag, guide cooling air, quiet road noise, and guard against debris and corrosion. EVs rely even more on full-length panels for range. Inspect after impacts, replace failed clips promptly, and use correct lift points to preserve both protection and performance.

What is the plastic underneath the car called?

The plastic cover underneath the car is generally called a splash shield, splash guard, engine splash shield, or underbody panel. This component protects the engine and other sensitive parts from road debris like water, dirt, and rocks, and also improves the vehicle’s aerodynamics.
 
Key purposes of a splash shield:

• Protection from debris: It acts as a barrier, preventing water, mud, sand, and small rocks from splashing onto the engine and other vital undercarriage components. 
• Component protection: It safeguards electronics, the engine, and other parts from damage and corrosion. 
• Aerodynamic benefits: The shield helps improve airflow underneath the car, reducing drag and potentially improving gas mileage. 

When to consider replacement: 

• If the splash shield is torn, broken, or dragging on the ground, it should be replaced to ensure continued protection and to prevent potential damage to the vehicle’s underside.

Can I drive with Splash Shield hanging?

No, you should not drive with a dragging splash shield, as it can cause damage to engine components, affect fuel economy, and pose a safety hazard to other vehicles. The best solution is to temporarily secure it with zip ties or remove the damaged portion, and then schedule a proper repair or replacement as soon as possible.
 
Why you shouldn’t drive with a dragging splash shield:

• Protects the engine compartment: The splash shield prevents water, dirt, and road debris from entering the engine compartment, which can cause corrosion and damage to crucial electrical components. 
• Improves aerodynamics: It contributes to proper airflow under the vehicle, which helps maintain good fuel economy. 
• Potential for further damage: A dragging or broken shield can snag on road debris or become a hazard for other drivers if it tears off completely. 
• Annoying noise: The dragging often creates a scraping noise that can be distracting and signals an underlying problem. 

What to do instead:

1. Temporarily secure the shield: Use zip ties or tape to hold the dragging part up or tie it in place to prevent further damage or detachment. 
2. Remove the damaged section: If the shield is significantly torn, you can use a hand saw, Dremel, or metal shears to cut off the loose piece to prevent it from hitting the ground. 
3. Get it repaired or replaced: Schedule an appointment with a mechanic to have the splash shield and its fasteners properly repaired or replaced to restore your vehicle’s protection and performance. 

What are the plastic pieces on the bottom of my car?

A vehicle’s engine splash shield is also called the skid plate, the engine splash guard, or the lower/under-engine cover. It’s a panel that’s designed to protect the underside of the vehicle’s engine and other important components from water, corrosive materials, and road debris.

What happens if an engine splash shield is damaged?

An intact splash shield provides proper airflow to your engine, helping it stay cool during operation. If the shield is damaged or misaligned, it can restrict airflow, causing your engine to overheat. That can lead to severe engine problems, which is why it’s so important that the shield functions effectively.