By the end of this topic, you should be able to...
discuss the classification of materials into natural and human-made, including for example timbers, polymers, metals, glass, textiles, composites, smart materials and biomaterials.
Guiding Question
How do material properties and classifications aid material selection for a specified manufacturing process?
💡 Did You Know? The wood in your bedroom furniture grew in a forest. The rubber in your trainers was tapped from a tree. The cotton in your t-shirt was harvested from a field. But the carbon fibre in a professional racing bike was synthesised in an industrial plant at temperatures exceeding 1,000°C, and the titanium screw holding a fractured bone together was engineered at the atomic level to bond with living tissue. Materials come from two fundamentally different places — nature and the laboratory — and that distinction matters enormously to a designer. It shapes sustainability decisions, manufacturing choices, regulatory obligations, and end-of-life strategies simultaneously. This sub-topic maps the full landscape of material types across that natural/human-made axis.
The Natural vs Human-Made Axis
In A3.1.1, materials were organised by family — metals, polymers, ceramics, composites, smart materials. This sub-topic adds a second, equally important classification axis: origin — whether a material is natural or human-made.
This is not always a clean binary. Many materials occupy an intermediate position:
Classification | Description | Example |
Purely natural | Grown or occurring in nature; minimal processing | Solid oak timber, raw wool fleece, natural rubber latex |
Processed from natural sources | Natural raw materials transformed by industrial processes | Steel (from iron ore), glass (from sand), copper (from ore) |
Modified natural materials | Natural materials chemically altered to improve properties | Vulcanised rubber, viscose (wood pulp → textile fibre) |
Bio-based synthetics | Synthesised industrially but from renewable biological feedstocks | PLA polymer (from corn starch) |
Fully synthetic | No natural equivalent; entirely engineered | Kevlar, Nitinol shape memory alloy, piezoelectric ceramics |
Key design insight:Â
The same material family can contain both natural and human-made members. Polymers include both natural rubber (grown in trees) and ABS (synthesised from crude oil). Textiles include both cotton (grown in fields) and Gore-Tex (manufactured in industrial plants). Composites include both wood (a natural composite) and CFRP (a precision-engineered composite). This is why the natural/human-made axis must be understood as distinct from the five-family classification.
Polymers
Composites
Metals and Alloys
Timbers
Textiles
Smart Materials
Biomaterials
Coming soon...
Advantages of the Natural/Human-Made Classification as a Design Tool
Using this classification explicitly during material selection provides several distinct advantages:
Sustainability prediction:Â Materials from renewable natural sources (timber, cotton, natural rubber) can regenerate within human timescales. Materials from non-renewable human-made processes (steel, synthetic polymers, smart materials) cannot. The classification is an immediate sustainability filter.
Property variability management: Natural materials vary intrinsically — two boards of oak from the same species have different grain, density, and knot distribution. Human-made materials are engineered to specification — every batch of Grade 304 stainless steel or ABS injection moulding grade meets a defined property specification. Designers working to tight tolerances must account for natural material variability.
End-of-life pathway selection:Â Natural materials are generally compostable, biodegradable, or recyclable through biological cycles. Most human-made polymers are not biodegradable. The natural/human-made classification directly shapes end-of-life strategy selection from the earliest design stages.
Regulatory implications:Â Biomaterials, food-contact materials, and medical-grade materials face regulatory testing requirements (ISO 10993, FDA approval, CE marking under the EU MDR) that are directly linked to human-made material content, processing chemicals, and additives. A natural collagen scaffold requires different regulatory documentation than a PEEK spinal implant.
Supply chain ethics: Natural materials involve agriculture, forestry, and animal husbandry — industries with significant labour ethics, land-use, and deforestation implications. Human-made materials involve extractive mining and chemical manufacturing with different but equally significant ethical dimensions. Identifying origin classification early enables designers to investigate the supply chain for the correct category of ethical risk.
Table 1: Natural vs Human-Made Classification Matrix
Material Type | Natural Members | Human-Made Members | Intermediate / Hybrid |
Timbers | Hardwoods (oak, maple), softwoods (pine, spruce) | MDF, plywood, glulam, LVL, CLT | — |
Polymers | Natural rubber, silk, wool, cellulose, casein | ABS, PET, PP, PC, epoxy resin, silicone | PLA (bio-based but synthetically processed), viscose (natural cellulose, chemical processing) |
Metals | Native gold, silver, copper (rare, geological) | All commercial metals (extracted, refined, alloyed) | — |
Glass | Obsidian (volcanic), Libyan desert glass (impact) | Soda-lime, borosilicate, Gorilla Glass, glass-ceramic | — |
Textiles | Cotton, wool, silk, linen, hemp | Polyester, nylon, Kevlar, elastane, Gore-Tex | Viscose, Lyocell (natural cellulose source, chemical processing) |
Composites | Wood, bone, bamboo, nacre | CFRP, fibreglass, concrete, reinforced concrete | — |
Smart Materials | None (natural analogues only: pine cone, squid skin) | Nitinol, piezoceramics, thermochromics, MR fluid, D3O | — |
Biomaterials | Collagen, silk sutures, chitosan, alginate, hydroxyapatite | Titanium implants, medical silicone, UHMWPE, PEEK, PLA screws | Bioglass (synthetic composition, biologically active at interface) |
Practice Questions
The command term for this learning objective is DISCUSS — "offer a considered and balanced review that includes a range of arguments, factors or hypotheses. Opinions or conclusions should be presented clearly and supported with appropriate evidence." Questions asking only "what is a composite?" are worth minimal marks. Full marks require you to discuss implications, trade-offs, and the nuances of classification in relation to a specific design context.
Question 1Â (4 marks)
A product designer is selecting a material for a long-span architectural roof structure. Identify one material from each of the following categories and discuss the suitability of each for this application: (a) metal, (b) timber (engineered), (c) composite.
Examiner's hint: (a) Structural steel — high strength and stiffness, excellent for long spans, well-understood design codes, weldable; but heavy, requires corrosion protection, significant embodied energy. (b) Glulam (glued laminated timber) — large sections possible from small timber inputs, can be manufactured to curved profiles, good strength-to-weight, sequesters carbon, architecturally expressive; but requires moisture protection, longer lead times, fire must be designed for (though char layer provides some protection). (c) GFRP or CFRP composite — extremely high specific stiffness and strength, formable to complex curved aerodynamic profiles, corrosion resistant; but very expensive (CFRP), complex manufacturing process, difficult to inspect for internal damage, thermoset matrix means difficult end-of-life recycling. Discussion should weigh these against each other in context of: span requirements, budget, aesthetics, structural loading, durability requirements, and sustainability priorities. A full answer resists a definitive "winner" and instead presents the trade-offs of each classification.
Question 2Â (6 marks)
A design team is developing a reusable water bottle for high-performance athletes. The bottle must be: lightweight, structurally robust, food-safe, thermally insulating, and designed for a circular economy end-of-life strategy. Discuss the suitability of materials from three different classifications for this application. For each classification, identify a specific material, explain its relevant properties, and evaluate its strengths and limitations in the context of all five design requirements.
Examiner's hint: This is a full 6-mark discussion requiring two marks per material. Suggested: (1) Metal (stainless steel 316L): lightweight relative to glass, structurally very robust (durable for lifetime), food-safe (passive layer, inert — no migration), thermally insulating if double-wall vacuum construction (excellent — industry standard for performance water bottles, e.g. Hydro Flask), circular economy — fully recyclable indefinitely. Limitation: heavier than polymer; manufacturing energy (vacuum double wall). (2) Polymer (HDPE or PP): very lightweight, food-safe (very low migration), robust, cheap; poor thermal insulation in single-wall construction; recyclable (thermoplastic, recycling codes well established) but downcycling occurs in practice. Limitation: fails thermal insulation requirement in simple construction. (3) Composite (CFRP): extremely lightweight (best specific stiffness/strength — used in performance cycling bottles), structurally excellent, food-safe (inert epoxy/carbon surface); poor thermal insulation without secondary insulation layer; MAJOR limitation — thermoset epoxy matrix is not recyclable; CFRP bottle at end of life goes to landfill or incineration — directly contradicts the circular economy requirement. Discussion should conclude: the circular economy requirement and the thermal insulation requirement together point most strongly toward the stainless steel double-wall vacuum classification — but the discussion should present these as trade-offs, not a simple hierarchy.
Sources
Ashby, M.F. (2011). Materials Selection in Mechanical Design. 4th edn. Butterworth-Heinemann, Oxford.
Callister, W.D. and Rethwisch, D.G. (2018). Materials Science and Engineering: An Introduction. 10th edn. Wiley, New York.
Duerig, T., Pelton, A. and Stöckel, D. (1999). 'An overview of nitinol medical applications.' Materials Science and Engineering: A, 273–275, pp. 149–160.
Ellen MacArthur Foundation (2017). A New Textiles Economy: Redesigning Fashion's Future. Ellen MacArthur Foundation, Cowes. Available at: www.ellenmacarthurfoundation.org
European Commission (2004). Regulation (EC) No 1935/2004 on Materials and Articles Intended to Come into Contact with Food. Official Journal of the European Union.
Green, M. and Karsh, J. (2012). The Case for Tall Wood Buildings. mgb Architecture + Design, Vancouver.
International Baccalaureate Organization (2024). Design Technology Guide: Diploma Programme. First Assessment 2027. IBO, Geneva.
Ulrich, K.T. and Eppinger, S.D. (2015). Product Design and Development. 6th edn. McGraw-Hill Education, New York.
Williams, D.F. (2008). 'On the mechanisms of biocompatibility.' Biomaterials, 29(20), pp. 2941–2953.
Linking Questions
Why is a good understanding of material properties important when designing structural systems? (A3.2)
When do the physical properties of materials restrict the ability to use certain prototyping techniques? (A2.2)
How do the properties of a material influence the choice of manufacturing techniques for a product? (A4.1)
How can the characteristics of a material limit the effectiveness of modelling and prototyping as designs are developed? (B2.2)
How important is an understanding of the mechanical properties of a material when considering structural and mechanical systems, and their applications? (A3.2, A3.3, B3.2, B3.3)
Which classifications of properties are important when developing electronic systems and their applications? (A3.4, B3.4)
How could the continued development of biodegradable materials influence designers’ ability to address aspects of design for sustainability and design for a circular economy? (C2.1, C2.2)
Why is a thorough understanding of materials key for effective product analysis and evaluation of products? (C3.1)
How do design decisions related to the properties of materials and components impact a product’s life-cycle analysis? (C3.2)