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This lesson covers the key criteria designers and manufacturers use when selecting materials for products, as required by the AQA GCSE Design and Technology specification (8552), Section 3.2.1. When designing any product, choosing the right material is one of the most important decisions. A poor material choice can lead to product failure, excessive cost, or environmental harm. Understanding these criteria will help you justify material choices in your NEA (Non-Exam Assessment) project and answer exam questions confidently.
The primary purpose of a material is to perform its required function. Functionality means the material must be fit for purpose — it must do the job it is intended to do.
| Functional Requirement | What to Consider | Example |
|---|---|---|
| Strength | Can it withstand the forces applied during use? | A bicycle frame must resist bending forces — aluminium alloy or steel is chosen |
| Durability | Will it last for the expected product lifetime? | Outdoor garden furniture needs weather-resistant materials like teak or HDPE |
| Flexibility | Does it need to bend without breaking? | A phone case needs some flexibility — silicone or TPU is ideal |
| Hardness | Must it resist scratching or wear? | Kitchen worktops use granite or laminated MDF for scratch resistance |
| Thermal properties | Does it need to insulate or conduct heat? | Saucepan handles use thermosetting plastic (e.g. Bakelite) to insulate from heat |
| Electrical properties | Must it conduct or insulate electricity? | Electrical cable cores use copper (conductor) with PVC coating (insulator) |
AQA Exam Tip: When asked to justify a material choice, always link the material's properties to the product's function. For example: "Stainless steel is suitable for a kitchen sink because it is corrosion-resistant, hard-wearing, and hygienic — all essential functional requirements for a product in constant contact with water."
Aesthetics refers to how a product looks and feels. The visual and tactile qualities of a material significantly influence consumer appeal and purchasing decisions.
Key aesthetic factors include:
Real-world example: Apple designs its MacBook laptops using anodised aluminium because it provides a premium feel, a sleek brushed finish, and a range of subtle colours — all contributing to the product's aesthetic appeal.
Designers must consider the environmental impact of material choices throughout the entire product life cycle.
| Environmental Factor | Description | Example |
|---|---|---|
| Recyclability | Can the material be recycled at end of life? | Aluminium is infinitely recyclable and widely collected |
| Biodegradability | Will it break down naturally? | PLA (polylactic acid) is a biodegradable bioplastic used for packaging |
| Carbon footprint | How much CO2 is produced during extraction, processing, and transport? | Locally sourced softwood has a lower carbon footprint than imported hardwood |
| Toxicity | Does production or disposal release harmful substances? | Lead-free solder is now standard due to the toxicity of lead |
| Sustainability | Is the raw material from a renewable or finite source? | FSC-certified timber comes from sustainably managed forests |
AQA Exam Tip: Environmental factors are increasingly tested in the exam. Be prepared to discuss the six Rs (reduce, reuse, recycle, refuse, repair, rethink) and how they influence material selection. A strong answer links specific environmental concerns to specific material properties.
Cost is always a factor in commercial product design. The material must be affordable within the product's target price point.
Cost considerations include:
Real-world example: IKEA uses particleboard with melamine coating for many furniture ranges because it is extremely cost-effective compared to solid timber, while still providing an acceptable aesthetic finish for the target market.
A material must be available in the required form, quantity, and timeframe.
In practice, material selection is always a compromise between multiple criteria. No single material is perfect in every respect. Designers use a selection matrix to weigh up the pros and cons.
| Criterion | Weighting | Material A (ABS) | Material B (Aluminium) | Material C (Oak) |
|---|---|---|---|---|
| Functionality | 30% | 7 | 9 | 6 |
| Aesthetics | 20% | 6 | 8 | 9 |
| Environmental | 20% | 4 | 7 | 8 |
| Cost | 20% | 8 | 5 | 4 |
| Availability | 10% | 9 | 8 | 6 |
| Weighted total | 6.5 | 7.5 | 6.6 |
In this example, aluminium scores highest overall, making it the best choice for this particular product based on the designer's priorities.
AQA Exam Tip: In the exam, you may be asked to evaluate material choices for a given scenario. Always consider at least THREE criteria (e.g. functionality, cost, and environmental impact) and explain how they interact. Simply listing properties without linking them to the product's requirements will not gain full marks.
Brief: A UK company is designing a children's road bike for ages 8 to 11, to retail at one hundred and eighty pounds. The target frame mass is under 1.8 kg. The frame must survive normal child use for at least five years.
Step 1 — Identify priorities (percent weighting):
Functionality (strength, weight) 30%
Cost 25%
Durability 20%
Environmental impact 15%
Aesthetics 10%
Step 2 — Shortlist materials: steel (chromoly 4130), aluminium alloy (6061 T6), carbon fibre reinforced polymer (CFRP), and bamboo-composite.
Step 3 — Score each material 1-10.
Criterion Steel Alum CFRP Bamboo
Functionality 7 8 10 6
Cost 8 9 3 6
Durability 9 8 7 6
Environmental 5 6 4 9
Aesthetics 6 7 9 8
Step 4 — Weighted totals. For aluminium:
(8 x 0.30) + (9 x 0.25) + (8 x 0.20) + (6 x 0.15) + (7 x 0.10) = 2.4 + 2.25 + 1.6 + 0.9 + 0.7 = 7.85
Repeat for the others:
Steel 7.25
Alum 7.85
CFRP 6.50
Bamboo 6.80
Step 5 — Interpret. Aluminium wins on the weighted matrix. It delivers the functional requirement (high strength-to-weight, 6061 yield stress around 240 MPa), fits the cost bracket (extruded tubes from commodity billet), survives child use (good corrosion resistance if anodised), and is 100% recyclable at end of life. CFRP is ruled out by cost despite its superior functionality; bamboo has strong environmental credentials but fails on durability for a bike that may be thrown on the ground.
Step 6 — Calculate the stress check. If a 30 kg child (weight 294 N) drops onto the top tube (say cross-section 60 mm squared), the peak stress is:
Stress = 294 / (60 x 10 to the -6) = 4.9 x 10 to the 6 Pa = 4.9 MPa
With a yield stress of 240 MPa the safety factor is almost 50 — well clear of any plastic deformation. The selection matrix and the stress check therefore agree: 6061 T6 aluminium alloy is the best choice for this children's bike frame.
Step 7 — Note the standard components. The frame accepts off-the-shelf stainless M8 bottom-bracket cups, a 1-1/8 inch threadless headset, and standard 27.2 mm seatpost — widely stocked and inexpensive, reducing overall build cost and allowing easy repairs as the child grows.
Misconception: "There is always a single best material for any product."
Reality: Material selection is a weighted compromise. The best material depends on how the designer prioritises the criteria — change the weightings and the winner can change. For a one-off premium product, CFRP might score highest because cost matters less. For a mass-market children's bike, aluminium wins because cost and availability dominate. In the exam, always state the context and priorities before naming a material — "for a mass-market product at 180 pounds, aluminium is most suitable because..." is far stronger than "aluminium is the best material".
Question (9 marks): Using at least three criteria, evaluate the selection of a suitable material for a picnic bench that will live outdoors in a UK public park for at least 10 years. [9 marks]
Grade 3-4 response:
A picnic bench needs to be strong so it does not break. Wood is natural. Plastic lasts a long time. Metal can rust. I would choose wood because it looks nice outdoors.
Examiner comment: Vague properties, no named materials, no criteria weighting, no environmental reasoning. Few marks.
Grade 5-6 response:
The material must be durable (weather resistant), strong (support several adults) and low maintenance. FSC-certified oak is an option: it is strong, looks attractive, and comes from managed forests, but requires oiling every year. Recycled HDPE lumber is maintenance-free, does not rot, and is made from reclaimed milk bottles — very eco-friendly. Galvanised steel frame with hardwood slats is a hybrid option — strong but more expensive. I would choose recycled HDPE lumber because the council has limited maintenance budget and HDPE lasts 20+ years without any care.
Examiner comment: Three criteria, three named materials with specific properties, clear choice with justification. Middle-band quality.
Grade 7-9 response:
A public picnic bench must meet at least five selection criteria: functionality (support four adults, total roughly 350 kg or 3430 N distributed across the seats), durability (survive UV, rain, frost and vandalism for 10+ years), cost (public funding, target about three hundred pounds per bench), environmental (low embodied carbon, recyclable at end of life), and social (accessible, safe for children, hygienic).
FSC-certified oak has strong functional and aesthetic credentials — a bending strength of around 100 MPa and an attractive natural appearance — but it requires annual oiling, costs roughly five hundred pounds per bench, and loses marks without regular maintenance. Recycled HDPE lumber has excellent durability (UV-stabilised, rot-proof, no painting), lower bending strength (around 25 MPa) which is compensated by making the slats thicker (45 mm), and scores highest on environmental criteria because each bench uses approximately 80 kg of reclaimed plastic bottles otherwise destined for landfill or ocean. Galvanised steel with hardwood slats is durable but the galvanising can flake over time and the steel is cold to sit on in winter — a social comfort issue. Aluminium with HDPE slats is corrosion-proof but more expensive and offers no significant durability gain over all-HDPE.
Standard components — M10 stainless coach bolts, nylon-insert lock nuts, polyurethane washers — fix the slats to the frame on every option.
Conclusion: Recycled HDPE lumber is the best choice. It meets the functional requirement by oversizing the cross-section (ribbing/depth effect), delivers a 20-year maintenance-free service life well beyond the 10-year target, scores highest on environmental criteria (reclaimed plastic, recyclable at end of life), and is warm to sit on and splinter-free for child safety. The only weakness — aesthetic — is mitigated by wood-grain-effect moulds. Oak is rejected on maintenance cost; galvanised steel on winter comfort; aluminium on cost.
Examiner comment: Five criteria with quantitative targets, four candidate materials with specific property values, standard components included, clear justified conclusion with explicit rejection of alternatives. Full marks.
This content is aligned with the AQA GCSE Design and Technology (8552) specification, Paper 1: Core technical principles — Selection of materials and forces. For the most accurate and up-to-date information, please refer to the official AQA specification document.