# A builder is choosing between two materials to use as insulation in the walls of a new house. Material A is a thick layer of foam with many trapped air pockets. Material B is a thin sheet of shiny metal foil. Explain how each material reduces the transfer of thermal energy into or out of the house, and suggest which material would be more effective as wall insulation.

> WJEC A-Level Physics (Wales) — 3.4 Thermal physics · Explain · 5 marks

> Thermal insulation in buildings reduces the rate at which thermal energy is transferred between the inside and outside of the building.

## Mark scheme (5 marks)

1. Material A (foam) reduces conduction because air is a poor conductor / thermal insulator
2. The trapped air also reduces convection because the air cannot circulate / move freely
3. Material B (shiny metal foil) reduces thermal radiation because shiny / reflective surfaces are poor emitters and poor absorbers of infrared radiation
4. Material A (foam) is the better insulator because conduction and convection are the dominant mechanisms of heat loss through a wall / radiation is a small contribution compared to conduction and convection
5. Metal foil (Material B) is a good conductor so it would actually increase conduction of thermal energy through the wall

## Key terms

- [thermal energy](https://www.gradenine.co.uk/glossary/thermal-energy)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-builder-is-choosing-between-two-725afe2e) · Published by Druglandscape Ltd.