Cost, availability, and sustainability are key constraints in material selection. Designers balance them against the material properties required by the design specification to choose an option that is technically suitable, economically viable, obtainable, and environmentally responsible.
In B3.1 Material selection, a material must first provide required performance, such as strength, durability, density, thermal resistance, or aesthetic qualities. Cost, availability, and sustainability then determine whether its use is practical across the product life cycle.
| Factor | Role in material selection | Example |
|---|---|---|
| Cost | Includes purchase price plus processing, tooling, transport, maintenance, and end-of-life costs. A cheap raw material may require expensive manufacturing. | Aluminium may cost more than mild steel, but its low density and corrosion resistance can reduce transport and maintenance costs. |
| Availability | Considers whether the material is obtainable in the required quantity, quality, dimensions, and stock form. Lead times, location, supply reliability, and manufacturing access matter. | A locally available timber may replace an imported species to reduce delays and transport. |
| Sustainability | Examines impacts across the life cycle, including extraction, embodied energy, waste, lifespan, repair, reuse, recycling, and disposal. | Recycled aluminium reduces demand for virgin ore and generally uses less energy than primary aluminium. |
These factors often create trade-offs. A durable material may have a higher initial cost but extend product life and reduce replacement. A biodegradable material may seem sustainable, but its benefit falls if processing is energy-intensive or transport distances are long.
A common misconception is that the cheapest or most recyclable material is automatically best. Selection requires a justified comparison against the complete design specification, rather than one isolated factor.
Exam technique: For an “explain” question, identify each factor and show how it changes a specific selection decision. For an “evaluate” question, compare advantages and disadvantages, apply them to the product context, and reach a justified conclusion about the most appropriate material.