Prototyping Materials and Processes: A Practical Reference

Prototyping materials fall into four families — plastics, metals, elastomers and composites — and each pairs naturally with a small set of manufacturing processes. Picking the material without picking the process is where most prototype budgets quietly disappear, because the same nylon part costs $40 printed and $900 machined.

This reference covers what each family is good for, how the common processes compare on cost, lead time and tolerance, when to prototype in the production material and when not to, and the specification details that determine whether a quote is accurate. If you want the decision framework rather than the catalogue, start with choosing the best material for your prototype.

Most prototypes start in plastic because iteration speed matters more than final properties. PLA is fine for shape and fit checks and nothing else. ABS and PC handle heat and impact well enough for hand testing. Nylon, especially SLS nylon, is the workhorse for functional parts — living hinges, snap fits and clips survive real use in it. Acrylic and clear resins cover light pipes and lenses.

Aluminum 6061 is the default prototype metal: easy to machine, strong for its weight, and it anodizes for a production-like finish. Steel appears when stiffness or wear matters and weight does not, stainless when corrosion or hygiene is part of the specification, and titanium mainly in medical, aerospace and premium consumer parts where the strength-to-weight cost premium is justified.

Elastomer prototypes are specified by durometer, not just material. A 40A silicone gasket and an 80A one are different products with the same description. For seals, also ask about compression set — how much the material stays deformed after being squeezed for weeks — because that is what fails in the field, not tensile strength. Cast urethane is the standard route for small runs of rubber-like parts before soft tooling exists.

Composites deserve caution in prototyping. Carbon fiber and glass-filled nylon deliver stiffness per gram that metals cannot, but their properties depend on fiber orientation, and layup changes are slow and expensive to iterate. Prove the geometry in an isotropic material first, then convert once the shape is stable.

Not at the start. Early prototypes exist to answer questions about geometry, ergonomics and function, and a printed stand-in answers most of them for a tenth of the cost. Move to the production material when the answer depends on the material itself.

Costs and timelines for these builds are broken down in how much a prototype costs, how to estimate prototype cost and how long a prototype takes.

Prototypes are built from four material families: plastics such as PLA, ABS, polycarbonate and nylon for enclosures and functional parts; metals such as aluminum, steel, stainless and titanium for load-bearing and thermal parts; elastomers such as silicone, TPU and cast urethane for seals and grips; and composites such as carbon fiber and glass-filled nylon for high stiffness at low weight. Plastics dominate early iterations because they are fast and inexpensive to change.

Aluminum 6061 is the better default: it machines faster, weighs about a third of steel, anodizes for a production-like finish and costs less to cut even though the raw stock is more expensive. Choose steel when stiffness, wear resistance or hardness matters more than weight, such as fixtures, load frames and wear surfaces, or when the production part will be steel and the test results have to transfer.

Only when the question being asked depends on the material. Fit, layout and ergonomics can be answered with cheap printed plastic. Structural testing, fatigue, thermal behavior, electrical properties and any regulatory or biocompatibility testing require the production material and, ideally, the production process, because printed parts behave differently from molded or machined parts.

FDM 3D printing in PLA or PETG is the lowest-cost route for geometry and fit checks, often under $100 per part with a one to three day turnaround. Cost rises through SLA and SLS printing, then CNC machining, then urethane casting and soft tooling. The cheapest overall program usually uses the cheapest process that can answer each question, rather than one process for everything.

Print when the part is geometrically complex, the tolerance requirement is loose, and you expect to change it again soon. Machine when you need the real material properties, tolerances tighter than about 0.1 mm, a smooth as-machined surface, or a metal part. Many programs print the enclosure and machine the one or two parts that carry load.

LA NPDT specifies materials against what each prototype has to prove, then builds them through in-house rapid prototyping and vetted machining and molding partners. Send us the part and the question it needs to answer, and we will tell you the cheapest way to answer it.