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IB Design Technology
SL · Lesson 36 · Material Properties
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Lesson 36 · Unit 5

Material Properties

Distinguish the physical, chemical and mechanical properties that determine whether a material can perform in context.

80 minutesA3.1.4–A3.1.6
Guiding question: Which material property matters—and how is it different from the property next to it?01
Today’s destination

By the end of class, you should be able to…

01

Classify properties

Sort a property as physical, chemical or mechanical.

02

Explain 19 required terms

Use precise language for each syllabus property.

03

Distinguish look-alikes

Separate strength/stiffness/toughness/hardness and elasticity/plasticity.

04

Apply properties

Choose relevant properties for a design context.

Success check: Explain the concept accurately, then use it to make a justified design decision.
A3.1.4–6 · precise technical vocabulary02
A3.1.4

Measured or observed without chemically changing the material.

PhysicalDensityMass per unit volume; affects weight for a given size.
PhysicalThermal expansionChange in dimensions as temperature changes.
PhysicalThermal conductivityAbility to transfer heat.
PhysicalMelting pointTemperature at which a solid becomes liquid.
PhysicalElectrical resistivityOpposition to electrical current.
PhysicalElectrical conductivityAbility to conduct electrical current.
Physical: density → electrical conductivity03
ρ
Density

Same volume, different mass.

Density matters when a product must balance portability, stability, inertia or perceived weight.

Design question: does the product benefit from being light—or from having enough mass to stay stable?
Density is not the same as strength04

Thermal expansion

A material may grow/shrink as temperature changes. Designers need allowances where fit or sealing matters.

Thermal conductivity

High conductivity transfers heat readily; low conductivity can insulate.

Melting point

Places a temperature limit on applications and some manufacturing processes.

Thermal expansion · conductivity · melting point05
Conductivity

Lets current flow

Higher electrical conductivity = easier current flow.

↔
Resistivity

Opposes current

Higher electrical resistivity = greater opposition to current.

Do not use the two terms as synonyms—they describe opposing electrical behaviours.
Electrical conductivity vs resistivity06
A3.1.5

How the material reacts chemically.

Corrosion resistance

Ability to resist deterioration caused by chemical/environmental attack.

Reactivity (food safe)

Tendency to react chemically; food-contact materials must not create unacceptable reactions/contamination.

Hygroscopy

Tendency to absorb moisture from the surrounding environment.

Flammability

Ease with which a material ignites and burns.

Chemical: corrosion · reactivity · hygroscopy · flammability07

Wooden bathroom cabinet

Repeated humidity changes can alter dimensions, surface quality and joints if the material absorbs moisture.

Hygroscopy is therefore a material-selection issue—not merely “waterproofing” as a vague label.

Use the property term that explains the behaviour08
A3.1.6

Strength depends on the direction/type of loading.

Tensile strength

Resistance to pulling forces that try to stretch / separate the material.

↔

Compressive strength

Resistance to squeezing/crushing forces.

Tension ≠ compression09

Strength

Resistance to failure under a specified type of load.

Stiffness

Resistance to deformation. A material may be strong yet flexible, or stiff yet brittle.

Toughness

Energy absorbed before fracture; relates to resistance to impact/crack propagation.

Hardness

Resistance to localized surface damage such as indentation, scratching or wear.

Exam trap: “hard” does not automatically mean “tough,” and “strong” does not automatically mean “stiff.”
Strength · stiffness · toughness · hardness10

Elasticity

Deformation is recoverable: remove the load and the material returns toward its original form.

→ load →

Plasticity

Deformation is permanent: remove the load and the new shape remains.

Recoverable vs permanent deformation11
Compression

Malleability

Can be shaped under compressive forces—classically into sheets or forms—without breaking.

↔
Tension

Ductility

Can be stretched/drawn under tensile forces—classically into wire—without breaking.

Malleability = compression · ductility = tension12
MechanicalTensile strengthResistance to being pulled apart.
MechanicalCompressive strengthResistance to crushing/squeezing.
MechanicalStiffnessResistance to elastic deformation under load.
MechanicalToughnessAbility to absorb energy before fracture.
MechanicalHardnessResistance to scratching, indentation or wear.
MechanicalMalleabilityAbility to deform under compression into sheets/shapes without breaking.
MechanicalElasticityAbility to return to original shape after load is removed.
MechanicalPlasticityAbility to undergo permanent deformation without breaking.
MechanicalDuctilityAbility to deform under tension, often into wire, without breaking.
A3.1.6 · all nine required mechanical properties13
Knowledge check

A reusable food container must not react undesirably with acidic food. Which property is most directly relevant?

Select the property that matches the requirement14
A material dents easily but rarely cracks under impact. Which two properties are being contrasted?
Hardness (resistance to indentation) and toughness (energy absorbed before fracture).
A wire is easy to draw into a long thin form. Which mechanical property?
Ductility—deformation under tension without breaking.
A polymer insulator is selected because it opposes current. Which physical property?
High electrical resistivity (and correspondingly low electrical conductivity).
Why is hygroscopy classified as a chemical property in the IB guide?
The guide places hygroscopy in the chemical-property group; use that course classification in this syllabus context.
A3.1.4–6 · precise retrieval15
Exit ticket

Before you leave…

1. Choose one pair of easily confused properties and explain the difference.
2. Identify one property that matters for a cooking utensil and justify it.
3. Identify one mechanical property that would matter for a flexible clip.
Next lesson

Composites, Smart Materials & Biodegradable Materials

Keep the evidence chain moving: user → research → decision → test.

Curriculum alignment
A3.1.4 physical properties: density, thermal expansion, thermal conductivity, melting point, electrical resistivity, electrical conductivity. A3.1.5 chemical: corrosion resistance, reactivity (food safe), hygroscopy, flammability. A3.1.6 mechanical: tensile/compressive strength, stiffness, toughness, hardness, malleability, elasticity, plasticity, ductility.
Lesson complete16 slides
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IB Design Technology SL · Lesson 3616