What Are Radiators Made Out Of? Materials Compared

Quick answer: what are radiators made out of?

Most radiators are made from steel, cast iron, or aluminum in home heating systems, and primarily aluminum (or older copper/brass) in automotive cooling. Each material changes how fast the radiator transfers heat, how long it stays warm after shutoff, how it handles corrosion, and how easy it is to repair.

• Home panel radiators: usually painted low-carbon steel with internal water channels and external fins.
• Traditional column radiators: commonly cast iron, valued for thermal mass and longevity.
• Lightweight home radiators: often aluminum, popular in low-water-volume systems.
• Car radiators: typically aluminum core with plastic end tanks; older/heavy-duty designs may use copper/brass.

Why radiator material matters in real-world performance

A radiator’s job is to move heat from hot water (or coolant) into room air (or outside air). Material selection influences three practical outcomes: response speed, heat retention, and durability.

Heat transfer speed

Higher thermal conductivity moves heat through the metal faster. As rough benchmarks at room temperature: copper ≈ 385 W/m·K, aluminum ≈ 205 W/m·K, and typical carbon steel ≈ 45–50 W/m·K. In practice, airflow, fin design, and surface area often matter as much as the base metal.

Thermal mass and comfort feel

Heavier materials (notably cast iron) store more heat. That means slower warm-up, but they can keep emitting heat longer after the boiler or circulator turns off—useful in drafty buildings or where steady comfort is preferred.

Corrosion and water chemistry

Closed-loop systems are generally stable, but oxygen ingress (from frequent top-ups, leaks, or non-barrier tubing) increases corrosion risk—especially for steel. Mixed-metal systems can also create galvanic corrosion if inhibitors are not used correctly. The practical takeaway: material choice should match your system’s water quality and maintenance habits.

Common materials in home heating radiators

Steel (panel and column radiators)

Steel is the most common material for modern hydronic panel radiators because it is strong, cost-effective, and easy to manufacture into thin panels with convector fins. Many are factory-finished with durable coatings (e.g., powder coat) to resist external corrosion.

• Best for: standard homes, renovations, cost-sensitive installs, and compact footprints.
• Watch-outs: oxygenated system water can accelerate internal rust; frequent draining/refilling increases risk.

Cast iron (traditional column radiators)

Cast iron radiators are heavy, thick, and known for longevity. Their standout feature is heat retention: once hot, they provide a steady, slow-cooling warmth. This can be desirable in older homes with intermittent boiler cycles.

• Best for: period properties, comfort-first heating, and long service life.
• Watch-outs: very heavy (floor loading and wall support matter); slower response to thermostat setbacks.

Aluminum (lightweight, fast-response radiators)

Aluminum radiators heat up and cool down quickly and can deliver high output with lower water volume. They are popular in systems designed for fast control response, such as modulating boilers and zone-heavy layouts.

• Best for: quick temperature control, low-water systems, and installations where weight matters.
• Watch-outs: needs compatible inhibitors in mixed-metal loops; avoid harsh chemicals not rated for aluminum.

Automotive radiators: aluminum vs copper/brass

In vehicles, “radiator” usually means an air-cooled heat exchanger for engine coolant. Modern cars overwhelmingly use aluminum radiators because they are light, cost-efficient at scale, and handle vibration well. Many designs pair an aluminum core with plastic end tanks to reduce weight and manufacturing cost.

Why aluminum dominates today

• Weight advantage: aluminum radiator assemblies can be substantially lighter than copper/brass equivalents, improving vehicle efficiency.
• Manufacturing: brazed aluminum cores are well-suited to automated production and consistent quality.
• Design flexibility: tube and fin geometry can be optimized to compensate for lower conductivity vs copper.

Where copper/brass still shows up

Copper/brass radiators are less common in modern passenger vehicles, but they remain relevant in certain restoration, specialty, and heavy-duty contexts. Copper’s high thermal conductivity is a real advantage on paper; in the field, repairability is often the deciding factor.

• Repair: copper/brass units are frequently easier to solder and service than thin aluminum cores.
• Use cases: classic cars, custom builds, and some industrial equipment.

What else radiators are made of besides the metal body

When people ask what radiators are made out of, they often mean the core metal—but performance and lifespan also depend on coatings, seals, and joinery.

Coatings and finishes

• Home radiators are typically finished with powder coat or enamel paint for corrosion resistance and cleanability.
• Automotive radiators may use protective coatings on fins/tubes; end tanks on many models are reinforced polymer.

Gaskets, valves, and fittings

Thermostatic radiator valves (TRVs), bleed valves, and unions are commonly brass with polymer seals. In cars, hose necks and tank crimps rely on gaskets designed for thermal cycling; leaks are often seal-related rather than metal failure.

Material comparison table: conductivity, weight, and practical tradeoffs

How to tell what your radiator is made of

If you are unsure what your radiator is made out of, these checks usually narrow it down quickly. Use common sense and avoid scratching visible finished surfaces.

1. Magnet test: a strong magnet typically sticks to steel and cast iron, but not to aluminum or copper/brass.
2. Weight and feel: cast iron is unmistakably heavy for its size; aluminum feels light and “hollow” by comparison.
3. Color at an unpainted edge (if visible): aluminum looks silvery; copper is reddish; brass is yellow-gold; steel is gray and may show rust at chips.
4. Automotive clue: if the side tanks are black plastic with crimped seams, the core is almost always aluminum.

Choosing the right radiator material for your needs

The “best” material depends on what you value most: responsiveness, stability, budget, weight, or ease of repair. The selections below keep the decision practical.

• Choose steel when you want a proven, cost-effective radiator with broad sizing options and straightforward replacements.
• Choose cast iron when you want “steady warmth,” high durability, and aesthetics suited to traditional interiors.
• Choose aluminum when fast response, low water volume, and lighter installation loads are priorities.
• For vehicles, choose aluminum for modern OEM-style performance; consider copper/brass when repairability and restoration originality matter more than weight.

Rule of thumb: if your system water quality is uncertain or you frequently need to top up, prioritize robust corrosion control (inhibitors, air elimination, leak repair) as much as the radiator material itself.

Maintenance tips by material (to extend radiator life)

Radiators fail more often from system conditions than from “bad metal.” These practices reduce the most common failure modes across materials.

Steel and cast iron

• Minimize oxygen entry: fix leaks, avoid frequent draining/refilling, and use barrier pipe where applicable.
• Bleed air when needed and confirm the system has working air elimination to reduce corrosion and noise.

Aluminum

• Use inhibitors approved for mixed-metal systems and avoid aggressive cleaners not rated for aluminum.
• Keep the loop stable: consistent water chemistry and fewer top-ups reduce long-term risk.

Automotive (all materials)

• Maintain correct coolant mix and change intervals to protect against corrosion and scale.
• Keep fins clear (bugs, debris) and straighten bent fins carefully to restore airflow.