Insulation: what are the options? - Heating, Insulation and Ventilation NZ
Insulation: what are the options?

Insulation: what are the options?

With all the different insulation materials on the market, how do you know which one is right for your home?

Words by Blair Grant

We all want to live in healthy homes that are warm in the winter, cool in the summer, and 'just right' during those in-between months.

What that means in practice is that we want to live in a well insulated home. The correct insulation is what makes a home comfortable to live in, no matter what the weather's doing outside.

Here’s what you need to know about the different insulating products available, and what options might be best for your home.

What is an R value?

Before considering the various insulating materials on offer, it's important to understand the primary metric used to measure their effectiveness as insulators: the R-value.

The R-value of a material is a measure of its thermal resistance or, in other words, its ability to resist heat flowing through it. The higher the R-value, therefore, the better the product is at insulating.

Resisting heat flows is important for keeping warm air inside when it's cold outside, and cool air inside when outside is hot. So while insulation is often thought of as something mostly important for winter, it's still effective in the summer months, keeping homes cooler and minimising the transfer of outside heat to the inside.

The R-value of a product depends on two factors: the thermal conductivity of the material itself and the thickness of said material. This means that for some materials with higher thermal conductivity (that is, those that don't resist heat flow well) the insulation needs to be thicker to make up for it and achieve the same overall R-value.

While there are other factors involved, this is what can partially account for the differences in cost between different materials; those with lower thermal conductivity require more material to achieve the same R-value and therefore insulating effectiveness.

The building code has certain minimum standards for insulation in New Zealand homes, depending on the geographic region the home is in.

That said, the level of insulation required by the building code is the absolute minimum; there’s no reason why you can’t add more. As a rule of thumb, the better insulated your house is, the healthier it’s going to be and the less you’re going to need to spend on heating and cooling it.

The right amount of insulation will depend, in part, on your home's geographic location, framing structure and design, and cladding.

What else is there to consider with insulation?

While the R-value is one of the most important factors in choosing an insulating material, there are others to consider.


Some insulation materials are non-combustible while others need to be kept clear of potential heat sources.


Some insulation materials such as glasswool shed potentially harmful dust, which requires masks to be used when installing. While you're not going to be spending much time in the walls or the roof cavity of your home, if you ever conduct future renovations or install different downlights, for example, this dust can spread.

For those with allergies or respiratory problems, other materials could be worth considering.

Reaction to moisture

Insulating materials react differently to moisture, with some losing their insulating properties when wet. Ideally you won’t have too much moisture to worry about in a newly built home, but it's something to consider if you’re building a home in an area where heavy and/or driving rain.

There are other factors beyond R-value to consider when choosing an insulation material.

Changes over time

How will the insulating material perform over time? Some materials sag with age, which effectively reduces their thickness and diminishes one half of the R-value equation, lowering their insulating capabilities.


Materials differ in their ability to dampen sound. Depending on the location of your house, this may or may not be a relevant factor, but for those building in cities, near highways or trains, or who engage in loud activities like drum practice, a better sound-insulating material could be worth it.

What are the different insulating materials?

The most common insulation materials used in New Zealand are of four kinds.

Fibreglass insulation

The most commonly used material, fibreglass — also known as glasswool — insulation. It's made from up to 85 per cent recycled glass, and sometimes has chemical binders added that offer anti-flame and anti-microbial properties.

Its benefits include cost-effectiveness, resistance to combustion and moisture (though it loses insulating value when wet). Regular glasswool insulation can also provide some sound insulation, though specially designed variations are available. It's also long lasting and won't rot.

Glasswool insulation has the potential to shed dust, so care must be taken when installing and/or disturbing existing insulation.

It can be used in walls, as well as ceiling or roof spaces. Some glasswool products can also be used as underfloor insulation.

Wool insulation

Wool insulation is a natural product sourced from sheep. As a renewable resource, wool is a popular choice for sustainability purposes. Insulation can be made from both virgin and recycled wool. Part of the manufacturing process includes treatment to stop mould and increase resistance to pests and fire.

Wool can be recycled at the end of its life, which can make it a good choice for those after a sustainable and environmentally friendly insulation material.

Wool needs to be kept dry, as it loses insulation value when wet, and must also be kept away from potential heat sources.

Wool insulation can be used in walls, ceilings and roofs, as well as under suspended floors.

Mineral wool insulation

Mineral wool, also known as rock wool, is created from stone and industrial waste. Most products have an average of 75 per cent post-industrial recycled content, which reduces the environmental impact of the material.

Mineral wool is resistant to moisture but should be kept dry for best performance. It's also resistant to rot, and is non-combustible.

Mineral wool can only be used in walls and ceiling cavities. It comes in mat or blanket form, but can also be blown into ceilings using specialist installation equipment.

Synthetic insulation

Polyester insulation is a man-made fibre, and sometimes contains plastic from recycled bottles. It doesn't rot and has a long life, but like most other materials needs to be kept dry to maintain its insulating characteristics.

A benefit of polyester is that it's soft to touch and doesn't shed fibres like glasswool insulation can. This can make it a good option for those with allergies. It can be used for insulation in walls, ceilings and roofs, as well as underfloor.

A common synthetic material used for underfloor insulation is polystyrene. It comes in the form of a board and can be easily cut to fit in the open spaces under floors. It's water resistant and extremely lightweight.

While it's often used for underfloor insulation, it can also be used in walls and ceilings. A unique feature of polystyrene is its relatively high thermal resistance compared with other materials, which can make it effective in spaces where there isn't as much room for thick materials.

To get started insulating your home, browse our range of insulation products, or contact an insulation installer today.

Recommended reading