How insulation works
Heat always travels towards cooler areas. Insulation works by reducing the amount of heat entering from outside your home when it’s hot, and trapping warmth inside when it’s cold outside. The highest percentage of heat transfer occurs via the roof and ceiling, so it’s most important to insulate here. Insulation materials work by affecting some or all of the below three ways of heat transfer.
Conduction is the direct transfer of heat through solid materials. A metal poker put into a fire is heated through conduction.
Convection involves the transport of heat via the movement of gases or liquids. You’ll feel convection taking place in a two-storey house — the heat rises from the lower floor to the top.
Radiation is the transfer of heat across space from a warm body to a cold one — an example is the heat emitted by a bar radiator.
Insulation can be grouped into three categories:
Bulk insulation contains fibres that trap tiny pockets of air, which resist heat flow because these air pockets are poor conductors.
Types of bulk insulation available include:
- Glasswool. (fibreglass)
- Natural wool* (often mixed with polyester)
- Polystyrene boards
- Loose fill (made of shredded or granulated material)
Some examples are:
- Cellulose fibre (made from recycled paper)
- Natural wool
- Granulated rockwool
* All come as batts or blankets.
Reflective insulation dramatically reduces infrared radiant heat transfer from a hot surface to a cooler one. It's available as:
- Foil sheets laminated onto paper
- Concertina-style foil
- as a multi-cell foil product (silver batts) — a structure made of two to four layers of foil with air spaces in between
- To reflect heat, foil insulation needs to face an air space of at least 25 mm.
Composite materials combine elements of the two other types.
- Batts or blankets with foil backing (foil side facing out)
- Foil-faced boards
Which is best?
While manufacturers of each type tend to talk up their product, experts say any insulation is preferable to none, and every material has its place. The product chosen usually depends on personal issues, such as:
- Whether it’s made from recycled material
- Where the insulation is being installed
- Who’s doing the installation (DIY or professional installers)