Picking the materials used in product design can feel overwhelming when you face endless options. Start with what your product must do: match strength, weight, heat, cost and manufacturing method, and the shortlist shrinks to metals, plastics or composites.
If you are new to the field, start with the overview of what is industrial design, then return here for the materials side.
| Item (ABS, a common thermoplastic) | Typical value |
|---|---|
| Density | 1.05 to 1.07 Mg/m^3 |
| Price | 2.1 to 2.3 USD/kg |
| Young’s modulus (stiffness) | 2.5 to 4.6 GPa |
| Strength after ultrasonic welding | Up to 95% of the original |
| Strength after hot plate welding | Up to 80% of the original |
These figures come from the ABS material record in lecture slides on the Ashby method. They describe one plastic, prices and data can change, so check the source before you rely on them.
How do you choose between materials used in product design?
Start from the job, not the material. A Zetwerk guide to metals, plastics and composites says there is no universal “best” material, and that the right choice depends on mechanical requirements, operating environment, budget, production volume and sustainability goals.
A design-for-manufacturing training module hosted on energy.gov frames the goal the same way: find a material that meets the product design requirements and can be manufactured economically. It also lists look, feel and sense of quality among the things material selection drives, so appearance counts as a requirement too.
Turn that into a checklist before you compare any datasheet:
- Mechanical needs: tensile strength, yield strength, impact resistance, hardness, fatigue life and wear resistance.
- Weight: lighter parts can cut energy use, transport cost and effort for the person holding the product.
- Environment: moisture, saltwater, chemicals, UV radiation, extreme temperatures and abrasion.
- Manufacturing process: machining, casting, moulding and lay-up each suit different materials.
- Total cost: tooling, processing, assembly, maintenance, transport and end-of-life disposal.
Cost needs care, because material cost is only part of the total product cost. A cheaper material can cost more over the product’s life if durability or maintenance becomes an issue. Manufacturing capabilities also often decide the most practical choice, which is why the guide to design for manufacturing pairs naturally with this one.
Metals: strength, heat resistance and weight
Metals are known for their strength, toughness and ability to withstand high temperatures. Common choices include steel, stainless steel, aluminum, copper, titanium and brass.
A useful first split is ferrous versus non-ferrous. Ferrous metals contain iron, such as steel and cast iron, while non-ferrous metals such as aluminum, magnesium and copper do not.
The same metal name can hide big differences. Carbon steel properties vary significantly with heat treatment, and small changes in a metal’s composition can have significant effects. Cold finishing also work-hardens steel, which makes it harder to form, so the finishing route belongs in your specification.
Metals tend to suit these jobs:
- Load-bearing structures and machine components
- Industrial equipment and pressure vessels
- Automotive chassis and aerospace structural parts
The trade-offs are weight, corrosion and machining cost. The Zetwerk guide lists higher weight than plastics or composites, potential corrosion and higher machining costs for some alloys as the main limits. Standards bodies such as ASTM International maintain numbering and classification codes for metal products, and you can use these when selecting and buying.
Plastics: light, formable and varied
Plastics are lightweight polymers with excellent corrosion resistance and design flexibility. Typical examples are ABS, polycarbonate, nylon, polypropylene, polyethylene, PEEK and PVC, and they show up in consumer products, medical devices and electronic housings.
The key divide is thermoplastic versus thermoset. Thermoplastics tend to be softer, are used at lower temperatures than thermosets, and can be recycled or reheated. Thermosets such as epoxies and vulcanized rubber cure irreversibly, so once cured they cannot be reused or reheated.
Temperature limits matter in practice. Amorphous thermoplastics such as polycarbonate and PMMA soften at the glass-transition temperature, so you should not use them in environments that exceed it.
ABS as a worked example
ABS is tough, resilient and easily moulded, and it is used for casings, telephones and small moulded parts such as computer mouse casings. It is also a handy prototyping material: compression moulded heavy gauge ABS is often used for prototype model making.
It has clear weak spots, though. ABS is hygroscopic, so it may need oven drying before thermoforming, and it has only limited chemical resistance with poor resistance to solvents. Joining matters as well: ultrasonic welding can reduce strength to 95% of the original, and hot plate welding to 80%.
Additives and limits
Plastics degrade in sunlight and air, so suppliers add helpers. UV stabilizers reduce light damage, antioxidants prevent the breakdown of polymer chains through reactions with oxygen, and flame retardants are critical for compliance with safety regulations.
Even with additives, expect lower strength and lower heat resistance than metals. Plastics can creep under continuous loads, and some grades have limited recyclability.
Composites and other material classes
Composites combine more than one material to create improved performance. Most structural composites are reinforcing fibers embedded in a polymer resin, such as carbon fiber reinforced polymer, glass fiber reinforced polymer or fiberglass laminates.
They earn their place where weight savings justify higher cost:
- Aircraft structures and spacecraft
- Wind turbine blades and marine components
- Sporting goods and high-performance vehicles
The price is more complex manufacturing, higher material cost, difficult repair, challenging recycling and longer production times. Benefits include extreme lightness, high stiffness, excellent fatigue resistance and tailorable mechanical properties.
Metals, plastics and composites are not the whole picture. The energy.gov module also lists ceramics and advanced materials, and the Ashby slides place glasses, elastomers and natural materials such as hemp, flax and cotton fibres in the same material map.
Metals, plastics and composites compared
The table gives a general rating for each family, based on the Zetwerk comparison. Treat it as a screening aid, because individual alloys and grades can sit well above or below these ratings.
| Property | Metals | Plastics | Composites |
|---|---|---|---|
| Strength | Excellent | Moderate | Excellent |
| Weight | Heavy to moderate | Very light | Extremely light |
| Corrosion resistance | Varies by alloy | Excellent | Excellent |
| Temperature resistance | Excellent | Moderate | Moderate to high |
| Manufacturing cost | Moderate | Low | High |
| Recyclability | Excellent | Good, depending on type | More difficult |
The ratings in this table come from the Zetwerk material selection guide; they are general and can change, so check the source before you rely on them.
Read the table by priority. Choose metals for maximum structural strength and temperature resistance, plastics for lightweight, low-cost, high-volume parts, and composites for the best strength with the least weight.
A simple shortlisting routine
You can apply the same logic to any product. The Ashby method describes it as screening and ranking: remove what cannot work, then rank what is left.
- Write down the requirements: load, temperature range, environment, appearance and expected volume.
- Screen out any family or grade that fails a hard limit, such as a plastic that would exceed its glass-transition temperature.
- Rank the survivors by weight, cost and how well they suit your manufacturing process.
- Check the joining, finishing and recycling consequences of your leading candidate.
- Prototype and test before you commit to tooling.
Do this alongside your early concept work. Rough thumbnails from product design sketching are a good place to note which material each part is likely to use, so the choice shapes the form from the start.
Frequently asked questions
Which material is strongest?
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High-strength metals such as steel and titanium offer excellent absolute strength, while carbon fiber composites provide exceptional strength relative to their weight, according to the Zetwerk guide.
Are composites always better than metals?
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No. Composites excel where weight savings are critical, but they typically cost more, require specialized manufacturing, and can be more difficult to repair and recycle.
Can plastic parts be recycled?
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It depends on the type. Thermoplastics can be recycled or reheated, but thermosets cannot be reused or reheated once cured, and recycling rates vary by resin type.
Why choose plastic over metal?
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Plastics reduce weight, resist corrosion and often lower production cost, which suits many non-structural and moderately loaded parts. Metals remain the usual choice for high-strength structural jobs.
