Plastic vs Metal — When Engineering Plastics Are the Better Choice

Weight Savings

Engineering plastics typically have a density of 1.0–1.5 g/cm³, compared to aluminum at 2.7 g/cm³ and steel at 7.8 g/cm³. A PEEK component weighs approximately 80% less than its steel equivalent and about 50% less than aluminum.

Weight reduction directly impacts energy consumption in moving systems, shipping costs, and ergonomics. In aerospace and automotive, every gram saved matters.

Corrosion Resistance

This is one of the greatest advantages of engineering plastics. Plastics don’t rust, don’t oxidize, and don’t need surface treatments for corrosion protection. Metal parts require plating, anodizing, or painting — adding cost and maintenance. With plastic parts, these costs simply don’t exist.

This is especially decisive in chemical processing, food industry, and marine applications.

Self-Lubrication

Many engineering plastics (POM, PA, PEEK, PTFE) function in sliding applications without external lubrication. Metal bearings and sliding surfaces require regular lubrication, adding maintenance costs and contamination risk — particularly problematic in food processing and cleanroom environments.

Electrical Insulation

Engineering plastics are natural electrical insulators. Replacing a metal component with plastic eliminates electrical conductivity risks and simplifies assembly — no separate insulating sleeves or coatings needed.

Machining Costs

CNC machining of plastics is often faster than metals. Plastics cut more easily, place less stress on tooling, and rarely require post-processing such as deburring or surface treatment. This translates directly to lower per-part costs, especially in small to medium production runs.

When Metal Is Still Better

Extreme loads: For structural load-bearing parts under very high stress, metals remain superior.

Temperatures above 300 °C: While PEEK handles 250 °C, most metals operate at much higher temperatures.

Thermal conductivity is critical: When a part must efficiently conduct heat (e.g., heat sinks), metals are unmatched.

Electrical conductivity needed: Obviously, electrically conductive applications cannot use plastic.

Comparison Table

Successful Metal-to-Plastic Conversions

Pump impellers: Stainless steel to PEEK — 75% lighter, no corrosion, longer service life in aggressive fluids.

Plain bearings: Bronze to POM — no lubrication needed, lower friction, extended maintenance intervals.

Seals and bushings: Metal to PTFE-based — better chemical resistance, lower friction, no galvanic corrosion.

Conclusion

Using engineering plastic instead of metal isn’t a compromise — it’s often the better engineering solution. The key is selecting the right material for the right application. When conditions allow plastic, the benefits in weight, corrosion resistance, self-lubrication, and cost are undeniable.