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What is Insulation and how does it work?

You’ve probably heard that insulating your geyser is a good investment, but did you know insulating your home is an even better investment that can save you money and energy. Find out what insulation is, why you need it, what it does and what type is best for your home.

how insulation works graphic

Do I need insulation?

In a word, yes. Insulation can help stay cool in summer and warm in winter, saving you money in the process.

What is insulation?

Insulation is a general term used to describe any type of material creating a barrier between the surfaces of adjacent bodies, that stops the transmission of heat, sound, electricity, and moisture. For the purpose of this article, we’re going to talk about thermal insulation.

In basic terms, thermal insulation is what keeps your coffee hot in an insulated mug and your hands warm in gloves.

How heat flows

To understand how insulation works, it is first necessary to explain the different ways heat flows.

Heat moves naturally in three ways, conduction, convection, and radiation. Physically, heat always moves from areas of high temperature to those at a lower temperature, which is why, in the cold external temperatures of winter, the warmth inside a building will try to escape through walls, windows, roof and floor.

What is Insulation and how does it work


Conduction is the transmission of heat through solids, liquids, and gases from a hot body to a cooler one (or from the hot part of an object to a cooler part) through direct contact.

For example, if you touch a hot plate you can feel the heat moving into your body.  This is called conduction, and it happens whenever hot things touch cooler ones.


Convection occurs in gases and liquids when heat is transferred by the hotter material moving into a cooler area.

For example, if a hot surface is in contact with cooler air, heat is conducted to the air. This air then becomes warmer and therefore less dense than the adjacent cooler air. The warmer, lighter air rises upwards and is replaced by cooler air, causing a continuous flow of air by natural convection – gradually removing heat from the hot surface to the air.


Radiation is the process of heat transfer through electromagnetic waves from a ‘hot’ surface to a ‘cold’ surface through the air.

Radiant energy moves through space without heating anything in between – the energy is only absorbed when its path is blocked by an object which absorbs the energy and converts it to heat. The most common example is radiant heat from the sun, which travels millions of miles through space, and only has any effect when it is blocked by an object such as a building.

How Does Insulation Work?

Insulation is a thermally resistant barrier that prevents the movement of thermal energy into and out of the house. In simple terms: Insulation helps increase the energy efficiency of your home by blocking heat from entering the home in the summer and keeping the heat in during the winter. It’s that simple and it really works.

Insulation is so effective that its cost is often paid for through energy savings in less than a year…and with the rising cost of electricity, savings may come even sooner!

How Does Insulation Work

Insulation types and their applications

Insulation products come in two main categories; bulk and reflective, which are sometimes combined into a composite material.

  • Bulk insulation mainly resists the transfer of heat, by trapping air in still pockets within its structure.

Bulk insulation includes materials such as glass wool, wool, cellulose fibre, polyester, and polystyrene.

Bulk insultion

  • Reflective insulation mainly resists radiant heat flow due to its high reflectivity and low emissivity.

Reflective insulation is usually shiny aluminium foil laminated onto paper or plastic and is available as sheets (sarking), concertina-type batts and multi-cell batts. Together these products are known as reflective foil laminates or RFL.

Reflective insulation

Choosing insulation

To compare the insulating ability of the products available, we need to look at their R-value, which measures resistance to heat flow. The higher the R-value, the higher the level of insulation.

When choosing the type of insulation, you need to consider the following in addition to the R-value:

  • The price per square metre
  • Must it be installed professionally, or can it be DIY?
  • Will the material fit within the space available?
  • Life cycle costs
  • Where will the insulation be installed, in the roof, floor or wall?

Additionally, compare the environmental benefits of different products. Ask about recycled content and how easily the product can be recycled after use. For example, some brands of glass wool, polyester and cellulose fibre insulation contain significant amounts of recycled material.

Types of House Insulation Materials

There are three major types of insulation used in homes: foam, fibreglass, and cellulose.

1. Foam insulation

Foam insulation comes in two different forms, which are spray and injection foam.

  • Spray foam is sprayed in an open cavity, like in new construction, attics, crawl spaces, rim joists, and pole barns, in a liquid state. The spray foam then expands and fills the cavity.
  • Injection foam is pumped into an existing cavity, like walls, which makes it great for insulating existing homes.

Spray foam can be either open-cell or closed-cell foam insulation.

  • Open-cell spray foam is very light and pliable due to its composition. As open-cell foam dries, the gas inside the cells escapes through openings in the cell’s wall resulting in foam that is light and pliable that shifts as it settles.
  • Closed-cell spray foam is a much more dense and heavy composition. It creates a dense surface that is more resistant to weathering and temperature change.

2. Fiberglass insulation

Fibreglass comes in batts and rolls. It can be placed in unfinished walls, floors, attics, and ceilings. Fibreglass insulation is fitted between studs, joists, and beams.

3. Cellulose Insulation

Cellulose can be either loose-fill or blown-in. It is best used in enclosed existing walls or open new wall cavities. Cellulose insulation can also be used on unfinished attic floors.

In Summary

Whether you are looking for roof insulation, underfloor insulation, or acoustic wall insulation, choosing the right product for your application is important.

No matter your needs, you can trust Eco-Insulation to provide you with the most advanced, customized solutions, for new construction insulation, home remodelling insulation and more.

Whether you want to learn more about what insulation is or how insulation works, or if you need to hire a local insulation company in South Africa, contact Eco-Insulation today!

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