Year 7 Design & Technologies · Materials and Technologies · 9m read

Materials — Properties and Selection

Have you ever wondered why your phone screen is glass instead of plastic, or why bridges use steel rather than wood? Materials aren't one-size-fits-all — each has unique strengths and weaknesses that make it perfect for some jobs and terrible for others. Learning to match materials to their purpose is what separates clever designs from ones that fall apart, and it's a skill you'll use whether you're engineering, building, or creating anything physical.

Learning objective: Identify and compare properties of materials and explain how properties influence design decisions.

By the end of this lesson you can:

I classify materials into four main groups: metals, polymers, woods, ceramics.
I define key material properties: strength, hardness, flexibility, conductivity.
I justify a material choice for a design based on required properties.

Choosing materials is choosing clothes for the weather. Raincoat for rain, wool for cold, cotton for heat. Designers pick materials by their properties to suit the job.

Material properties and classification

FOUR MAIN MATERIAL GROUPS:

METALS:
Properties: high strength, conductors of heat and electricity, malleable, ductile.
FERROUS (contain iron): steel, cast iron. Magnetic. Can rust.
NON-FERROUS: aluminium, copper, brass. Won't rust (or very slowly).
Uses: structural (steel beams), electrical (copper wiring), lightweight structures (aluminium).

POLYMERS (plastics):
Made from long chains of molecules (petrochemicals). Very diverse properties.
THERMOPLASTICS: soften when heated, harden when cooled. Recyclable. (PET, HDPE, ABS).
THERMOSETS: set permanently when heated. Cannot be reheated/reformed. (Epoxy, Bakelite).
Properties: lightweight, corrosion-resistant, electrical insulators, can be transparent or opaque.

WOODS:
HARDWOODS: from deciduous trees (slow-growing). Oak, mahogany, teak. Dense, durable, beautiful grain.
SOFTWOODS: from coniferous trees (faster-growing). Pine, cedar. Lighter, cheaper, easier to work.
MANUFACTURED BOARDS: plywood (layers), MDF (fibres + resin), particleboard. Stable, no grain direction.

CERAMICS:
Inorganic, non-metallic materials. Clay, glass, porcelain, concrete, bricks.
Properties: hard, brittle (fracture without bending), excellent heat/electrical insulators, high compressive strength.
Uses: pottery, building materials, cutting tools (harder than metal), electronics insulation.

KEY MATERIAL PROPERTIES:
TENSILE STRENGTH: resistance to being pulled apart.
COMPRESSIVE STRENGTH: resistance to being squashed.
HARDNESS: resistance to surface scratching.
FLEXIBILITY/ELASTICITY: ability to bend and return to original shape.
TOUGHNESS: resistance to impact/sudden force.
CONDUCTIVITY: ability to transmit heat or electricity.
CORROSION RESISTANCE: resistance to rust/oxidation.

Material selection rules

Match property to function: A material's USE must match its PROPERTIES. A bridge needs high tensile and compressive strength. A frying pan needs thermal conductivity. Match function to property.
Consider all constraints: Properties are not the only factor: cost, availability, machinability (can it be cut/shaped?), sustainability, weight and aesthetics all matter.
Test properties systematically: Properties can be tested: hardness (scratch test with known materials), tensile strength (weights until breaking), flexibility (bend test), conductivity (circuit test).

Quick reference

| Material | Properties | Uses |
|---|---|---|
| Timber | Strong, renewable, workable | Furniture |
| Metal | Strong, conducts heat | Tools, frames |
| Plastic | Light, waterproof, mouldable | Containers |
| Textiles | Flexible, soft | Clothing |
| Card | Cheap, easy to cut | Prototypes |

Worked example (Medium)

Choose and justify a material for each: (A) a children's outdoor playground equipment, (B) electrical wire insulation.

A: Playground equipment. HIGH-DENSITY POLYETHYLENE (HDPE) or powder-coated steel. Needs: weather resistance, impact toughness (won't shatter), non-toxic if touched, UV resistant. Steel adds structural strength for play loads.
B: Wire insulation. PVC (polyvinyl chloride) plastic. Needs: electrical insulator (non-conductor), flexible (cable must bend), chemical resistance, doesn't corrode, colour-coded for safety.

Answer: A: HDPE/coated steel — weather and impact resistant. B: PVC — electrical insulator, flexible, durable.

Worked example (Hard)

Apply advanced understanding of materials — properties and selection to a challenging real-world scenario. Demonstrate systematic analysis using key concepts from this topic.

Analyse the context. Identify the key principles of materials — properties and selection that are relevant. Consider what specific knowledge is needed to address this scenario.
Apply specific knowledge. Use precise design and engineering terminology to analyse the situation. Show how concepts interact and build upon each other.
Evaluate implications. Consider the broader significance. How does this analysis connect to other aspects of design tech?
Form a conclusion. Synthesise your analysis into a well-reasoned conclusion supported by specific evidence and terminology.

Answer: Analysis demonstrates deep understanding of materials — properties and selection with specific terminology, systematic reasoning, and real-world application.

Common mistakes

Providing surface-level responses without depth Students state facts about materials — properties and selection without explaining underlying mechanisms, reasoning, or significance. Fix: Always explain WHY and HOW, not just WHAT. In design and technology assessments, depth of explanation distinguishes high-achieving responses from basic recall.
Not using precise design and engineering terminology Students use everyday language when specific terms would demonstrate stronger understanding. Fix: Build and use a vocabulary of key terms for this topic. Precise terminology shows understanding and earns higher marks in design and technology assessments.

Materials — Properties and Selection — connecting to the bigger picture

Understanding materials — properties and selection extends beyond this single topic — it connects to broader themes across design tech and other disciplines. Recognising these connections transforms isolated knowledge into an integrated framework that supports deeper analysis and creative problem-solving.

In professional practice, experts use conceptual frameworks — organised structures of related ideas — to approach new problems efficiently. They don't recall every fact; they activate connections between concepts that help them identify what's relevant. This is why the most effective study approach is not memorising more facts, but building richer connections between the facts you already know.

Active learning strategies that build these connections include: relating new concepts to personal experience, comparing ideas across different topics, applying knowledge to unfamiliar scenarios, and teaching concepts to others. Each of these forces you to process information more deeply than passive reading or highlighting. The goal is to develop the kind of flexible understanding that allows you to analyse any question about materials — properties and selection — even ones you haven't seen before — by drawing on a network of connected ideas.

Practice questions

A thermoplastic can be reheated and reshaped. This makes it useful for:
1. Electrical insulators that must be permanent
2. Recycling and remoulding into new products
3. High-temperature cooking equipment
4. Load-bearing structural beams
(1 marks)
Explain why steel is preferred over wood for building a bridge that must carry heavy vehicles.
(2 marks)

Summary

Classify materials into four main groups: metals, polymers, woods, ceramics.
Define key material properties: strength, hardness, flexibility, conductivity.
Justify a material choice for a design based on required properties.