Choosing a material for a new product means satisfying seven things at once — mechanical load, operating environment, manufacturing process, total cost, supply availability, look and feel, and regulatory requirements — and no single material wins on all of them. The right method is not to search for the "best" material but to write down the constraints, eliminate everything that cannot meet the hard ones, and then choose among the survivors on the soft ones. Material choice locks in your manufacturing process, your unit cost, and your product's failure mode, which is why it deserves a deliberate decision rather than a default.
One decision that affects everything downstream
Material and process are inseparable. Choosing a glass-filled nylon commits you to molding and to a tool. Choosing sheet aluminum commits you to bending, punching, and finishing. Change the material late and you often change the process, which changes the tooling, the supplier, the lead time, and the price — a chain reaction that arrives exactly when you have the least schedule left.
The seven criteria
1. Mechanical load
What forces does the part carry, in what direction, how many times, and what happens if it fails? Distinguish stiffness (resistance to bending) from strength (resistance to breaking) from toughness (energy absorbed before fracture). A part that must survive impact needs toughness, not just a high strength number — the exact reasoning behind designing for drop test survival. Also consider creep: plastics under sustained load deform slowly over time, so a bracket that holds weight for years is a different problem from one loaded briefly.
2. Operating environment
Temperature range, humidity, UV exposure, water, cleaning chemicals, oils, food contact, skin contact. Outdoor products need UV-stable materials or they chalk and crack. Nylon absorbs moisture and grows. Many plastics are attacked by common disinfectants, which matters enormously for anything used in a clinic or kitchen.
3. Manufacturing process
Not every material can be made every way. Injection molding needs a thermoplastic with appropriate flow; die casting needs a castable alloy; machining favors free-cutting metals and rigid plastics. Because process choice is volume-driven, work through choosing a manufacturing process by volume in parallel with material selection rather than after it.
4. Cost — and not only of the material
Raw material price per pound is the least important part of the cost picture. What matters is total part cost: material volume, cycle time, tooling, secondary operations, finishing, scrap rate, and assembly labor. An expensive engineering plastic that molds faster and needs no painting can be cheaper per finished part than a cheap commodity resin that requires a coating. This is standard ground in value engineering.
5. Availability and supply chain
Can you buy it, in your color, in the quantity you need, from more than one source? Specialty grades with single suppliers and long lead times are a genuine business risk. Whenever practical, qualify a second source before production, not during a shortage.
6. Look and feel
Gloss, texture, translucency, colorability, weight in the hand, sound when tapped, warmth to the touch. Users judge quality through material, and heavier products are perceived as better made whether or not that is true. This is where material selection overlaps with industrial design, and where a decision that looks purely aesthetic turns out to constrain the process.
7. Standards and safety
Flammability ratings for enclosures around electrical parts, food-contact suitability for anything touching food, biocompatibility for skin or tissue contact, and restricted-substance limits for consumer goods. These are pass or fail requirements, so they belong in the eliminate step, not the compare step. Depending on the product, food-grade plastics or biocompatibility requirements may set the boundary. Nothing here is regulatory advice; confirm applicable requirements for your product with a qualified specialist.
A practical selection method
- Write the hard constraints. Temperature limits, contact requirements, flammability, maximum unit cost, process. These eliminate, and they are not negotiable.
- Generate a shortlist of three to five candidates that pass every hard constraint. More than five means your constraints are too loose.
- Score the shortlist on the soft criteria — cost, appearance, availability, ease of processing — weighted by what matters for this product.
- Get real datasheets for specific grades, not generic family averages. "ABS" covers dozens of grades with meaningfully different properties.
- Ask your manufacturer. A molder who runs a resin daily knows things no datasheet contains, including which grades warp and which colors are actually stocked.
- Test in the real material before design freeze, under the real environment, for long enough to see creep and chemical effects.
Three families worth knowing
- Commodity thermoplastics — polypropylene, polyethylene, ABS, polystyrene. Inexpensive, easy to mold, adequate for most consumer housings. ABS is the default for a reason.
- Engineering thermoplastics — polycarbonate, nylon, acetal, PC/ABS, and glass-filled variants. Stronger, tougher, more temperature-capable, and more expensive; the ABS versus polycarbonate comparison is the most common decision in this group.
- Metals — aluminum for light stiff parts and heat spreading, steel for strength and wear, stainless for corrosion and hygiene. The tradeoffs are laid out in aluminum versus steel.
For plastics specifically, our guide to choosing a plastic for your product goes grade by grade.
The most common trap: prototyping in a different material
A 3D printed prototype is not made of the material your product will be made of, even when the spool says the same three letters. Printed parts are layered, anisotropic, and usually weaker along the build direction, while molded parts are dense and directionally influenced by flow instead. A printed part that survives your test tells you the geometry is plausible; it does not tell you the molded part will pass, and a printed part that breaks may still be fine in production. Understand the difference — see 3D printing materials — and validate load-bearing parts in production material or by machining from the real stock before you commit to a tool.
Weighing materials for a part and unsure which constraint should win? Describe the application through our contact form and we will help you narrow it to a shortlist you can test.