GCSE PHYSICS - How Trapped Air is used for Heat Insulation in Buildings - How does Cavity Wall Insulation Work?

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How is Trapped Air used for Heat Insulation in Buildings?

Trapped air can be used in various ways to insulate buildings.

Examples are loft insulation, hot water tank and pipe insulation,
double glazing and cavity wall insulation (see below).

How does Cavity Wall Insulation Work?

Many houses are built with cavity walls. There is an
outside wall and an inside wall with an air gap between the
two walls. This is a good way of preventing the inside wall
of the house from becoming damp but the air gap
can transfer heat by convection making the house colder.

Cavity wall insulation fills the air gap with a polymer foam.
The foam is a type of plastic material that has air trapped inside
it. The foam replaces the air in the gap between the bricks.

Cavity Wall Insulation

No heat can now be transferred by convection because the air
has been replaced by foam. Conduction is very poor because
both the polymer and the trapped air are good insulators.
The room in the house stays warmer for longer (see costs).

Other examples of a polymer containing trapped air are
bubble-wrap and polystyrene foam. They are both
used for packaging because they have a low density.
Polystyrene foam is also used to make disposable cups for
hot drinks machines. The outside of the cup is cool enough
to pick up although the inside may contain hot tea or coffee.

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