Insulation materials
Find the right insulation material for your purpose.
A wide range of insulation materials is available - each with different properties and features, and each suitable for different parts of the house.
Increasingly, insulation products are available containing recycled material, such as wool, or in fully recycled formats such as polystyrene sheets.
Things to consider
R value
The ‘R value’ measures how good the insulation material is at containing heat. The higher the R value, the better the insulation will be. The insulation needs to be properly installed to reach the R value.
The Building Code specifies minimum R values for floor, wall and ceilings - it’s a very good idea to exceed the minimum requirements to get a warmer home needing less energy to heat.
See the main insulation page for more.
Cost
When comparing prices, you’ll need to consider the R value you’re aiming to achieve, and the amount of insulation you’ll need to achieve that R value across the whole area you’re insulating. That will give you a price for the insulation materials for the whole job.
The price per square metre or per kilogram on its own may be misleading if you’re comparing different types, formats, or thicknesses of insulation - for example, wool against polystyrene, or blanket insulation against loose fill. Or if you are comparing different R values.
Don’t forget installation costs if you aren’t doing it yourself.
Some insulation products are made to measure, others are fixed sizes. Fixed size products may increase the amount of wastage if you can use the offcuts, for example, you may not be able to use polystyrene off cuts.
Reflective insulation uses staples and strapping makes up a large percentage of the overall cost, so don’t forget to include this in calculations if you are installing this yourself.
When you buy insulation, check that you can return unopened bags if you have any left over.
Labelling
All insulation should be labelled with the following information:
- description of contents
- R value with the conditions under which the R value applies
- safety and handling instructions
- installation instructions
- fire safety.
Blankets and segments should also have information on thickness, length, width and coverage area of the pack. Some products may have acoustic (noise) ratings.
Loose fill insulation should state the thickness of fill required to get the stated R value.
The R value for reflective insulation is based the product being correctly installed, whereas for all other products the R value is the value of the material itself. So the need for an air gap for reflective insulation to be effective is included in the R value for this type of insulation. However, if you install polystyrene with an air gap although you will increase the insulation properties, this will not be included in the R value.
Long-term environmental impact
When you’re comparing insulation materials, consider:
- how much recycled content the insulation has - recycled content is becoming increasingly common
- whether the material can be recycled at the end of the building’s life
- how long it lasts for
- direct environmental impacts from processing the raw materials involved in making the insulation
- how much processing is needed to make it - more processing will mean more energy is used.
The environmental impacts of a particular material can be weighed up against the amount of insulation it provides and the energy saving benefits from its use. Studies have shown that the benefits of insulation in reducing home energy use clearly outweigh the energy consumed in the manufacture.
See the sections on embodied energy> Embodied energy --> and life-cycle analysis> Life-cycle analysis --> for more information about assessing long-term environmental impacts of building materials.
Additional information
Ask suppliers for product data sheets for more information on how the product is made, what it contains and how it performs.
Wool insulation
What is it?
Wool insulation is made from natural sheep wool (either new or recycled), and may be blended with preservatives, and polyester or resin. Blending is needed to give added strength so the insulation keeps its shape and doesn’t slump in wall cavities over time.
It is also treated to make it pest, mould, fire and slump resistant.
Wool-based insulation can only be labelled as “wool” if it contains more than 95% natural wool.
Polyester/wool blends are available using up to 40% polyester or recycled plastic fibre mixed with recycled or virgin wool.
Format
Wool insulation comes in blankets, loose fill, and segments.
Toxicity/emissions/air quality issues
Wool itself is not toxic. However, it pays to research what it has been blended with. Some resins or binding products could potentially have low levels of emissions when first installed - check with the supplier. Wool insulation is non-irritating and easy to handle.
Recyclability/re-usability/waste minimisation
Wool insulation may be recyclable, depending on what it has been blended with.
Some wool insulation products have up to 100% recycled wool content.
Sourcing
Wool insulation is New Zealand-made. There are a number of suppliers, making different products and formats.
Sustainability
Wool is a sustainable agricultural by-product .
Efficiency/functionality
Wool will lose effectiveness as it gets wet. However, once it dries again it will regain its effectiveness and it can cope with repeated wetting and drying. It will also retain some insulating properties until it reaches saturation.
Wool insulation is available with enhanced noise prevention properties.
It is available in a variety of formats, and is effective as an insulation material in walls, under floors and ceilings.
Approximate R value for a 100mm-thick blanket or segment is 1.8 to 2.3. Approximate R value for 150mm of loose fill is 2.5 when applied at 15kg/m2.
Polystyrene
What is it?
Polystyrene is a highly processed, synthetic material based on petro-chemicals. Fire retardant is added during manufacture.
It is used as stable, rigid foam that can be formed or cut into a range of shapes and thicknesses.
Polystyrene foam is available as extruded, or expanded (commonly seen white format). Extruded polystyrene is less bulky, but more expensive, and used for specialist situations and construction systems.
Format
Polystyrene insulation comes in rigid sheets and planks which can be used in underfloor slabs, in exterior walls as cladding and insulation, and in ceilings.
You can also get polystyrene “pods” for use in concrete flooring, and polystyrene insulation can be used in ‘sandwich’ format in preformed concrete slabs and blocks (where the concrete fills a cavity between polystyrene sheets).
Toxicity/emissions/air quality issues
Polystyrene is toxic if burnt.
Extruded polystyrene may emit a form of CFC (CFCs deplete the ozone layer).
It’s safe if fully sealed by concrete or cladding, so any emissions are contained.
Polystyrene is easy to handle but shreds and crumbs from cutting should not be inhaled. They should be contained and prevented from entering soil and water as they break down very slowly.
Recyclability/re-usability/waste minimisation
Polystyrene can be recycled for insulation if it has not been broken up. Recycled polystyrene is available through specialised suppliers or through regional waste recovery centres.
Where possible, use recycled polystyrene sheets for slab insulation.
Sourcing
Polystyrene is either imported, or polystyrene base material is imported and further processed in New Zealand. It can be sourced throughout New Zealand from recyclers, installers and manufacturers.
Some extruded polystyrene sheeting may be imported.
Sustainability
Polystyrene is manufactured from a by-product of the petrochemical industry. It’s more sustainable to use insulation made from recycled polystyrene than to use insulation made from new polystyrene.
Efficiency/functionality
Polystyrene is a very effective and widely used form of insulation.
Approximate R value for 100mm-thick polystyrene is 2.5 to 3.0.
Glass and mineral wools
What is it?
Glass and mineral wool types of insulation are made from materials such as rock slag, recycled glass, quartz sand, soda ash, limestone, and boron which are melted and spun into fibres.
Mineral wool can contain up to 15% of industry mineral waste. Glass/fibreglass insulation can contain up to 80% recycled glass.
Format
Glass and mineral wool insulation comes in blankets, segments and loose fill.
Toxicity/emissions/air quality issues
These products don’t emit any harmful airborne pollutants.
You may get some dust from loose fill glass wool insulation, both during installation and afterwards. Mineral wool is generally dust-free.
When you’re installing glass wool insulation, you should use protective clothing and a mask or respirator to prevent inhalation of small fibres and minor skin irritation.
Recyclability/re-usability/waste minimisation
If kept dry, glass-based insulation can be recycled. The recycled content contributes to overall minimisation of glass and mineral waste.
Sourcing
Glass and mineral wool insulation are both made in New Zealand and imported. There are a number of suppliers, offering a range of formats.
Sustainability
The base materials used to make glass and mineral wool insulation are non-renewable. Increasing the recycled content of glass wool significantly improves the sustainability.
Efficiency/functionality
Glass and mineral wool will melt, rather than burn, in a hot fire.
Glass wool insulation is available with enhanced noise prevention properties.
As with all insulation, glass and mineral wool is less effective if wet, but insulation properties are restored as soon as it dries. Over repeated wetting, glass and mineral wool insulation will lose its effectiveness.
Glass and mineral wool is a very effective and widely used form of insulation.
Approximate R value for 100mm-thick glass or mineral wool insulation is 2.6.
Paper-based (cellulosic) insulation
What is it?
Paper-based or cellulosic (wood-based) insulation is made from paper or paper-board. Recycled content can be up to 100%.
Fire-retardants and pest retardants are mixed with the paper, and can be up to 35% of the insulation mix.
Format
This type of insulation is available only as loose fill.
Toxicity/emissions/air quality issues
High levels of dust may be generated from installation and use. Protection from dust may be required.
Recyclability/re-usability/waste minimisation
Recycled paper can be used for this insulation.
The loose fill insulation cannot be recycled due to the addition of fire-retardant chemicals.
Sourcing
Paper-based insulation is New Zealand-made. There are a number of suppliers.
Sustainability
The base material for this type of insulation is wood or recycled paper. These are sustainable options so long as the wood base is derived from sustainable sources such as New Zealand-grown pinus radiata.
Efficiency/functionality
This is type of insulation is often used for existing houses where installing blanket insulation would be too difficult.
This type of insulation can slump in walls over a number of years, and will become ineffective if it gets damp.
Approximate R value for 100mm is 2.5.
Polyester
What is it?
Polyester is a synthetic material based on petrochemicals. To ensure it holds its shape, it is either heat-treated or adhesive binding agents are added.
Some 100%-polyester products may contain recycled polyester fibre.
Polyester/wool blends are available using up to 40% polyester or recycled plastic fibre mixed with recycled or virgin wool.
Format
Polyester insulation comes in blankets, segments, and loose fill.
Toxicity/emissions/air quality issues
Polyester insulation will not emit any airborne pollutants if no chemical binders are used.
It is toxic if burnt.
Dust masks are recommended during installation.
Recyclability/re-usability/waste minimisation
Polyester/wool blends can contain a high proportion of both recycled wool and polyester off-cuts, contributing to general waste minimisation.
Polyester insulation does not degrade and is claimed to be suitable to recycle and re-use.
Sourcing
There are several companies in New Zealand manufacturing and distributing polyester insulation.
Sustainability
This is a by-product of the petrochemical industry. It’s more sustainable to use insulation containing recycled polyester than to use insulation made from new polyester.
Efficiency/functionality
Polyester is a cost-effective and widely used form of insulation.
As with other bulk insulation, polyester needs time to restore its natural loft after being packed and stored. Longer storage time will require a longer loft restoration time.
It loses its effectiveness as soon as it gets wet, but insulation properties are restored when it dries.
Polyester does not burn easily, but will smoke.
Approximate R value for 100mm is 1.8 to 2.
Reflective
What is it?
Reflective insulation is a flexible sheet of metallic foil which may be used as the outer layers of a sandwich with other insulating materials bonded between it.
Format
Reflective insulation comes in foil blankets which can be perforated, multiple layer, reflective on one or both sides. It is a product in its own right but works well in combination with bulk insulation such as wool or mineral wool in under floor situations.
Reflective insulation can also be bonded to various bulk blanket insulation materials such as glass fibre or wool.
WARNING: Installing underfloor foil insulation can be risky. Be careful not to pierce electrical cabling with staples. Existing foil insulation, if improperly installed, can be live. If you are unsure about anything, hire a professional installer or get an electrician to check things out.
Toxicity/emissions/air quality issues
There are no emissions from reflective insulation.
Recyclability/re-usability/waste minimisation
Reflective insulation deteriorates over time, particularly if dust settles on the foil surface. Recycling is not feasible and reuse is not common.
Sourcing
Reflective insulation is manufactured and supplied in New Zealand.
Efficiency/functionality
Reflective insulation can be highly effective as a radiant heat barrier, and as a moisture/vapour barrier, although this is not required in New Zealand houses.
It works well under the floor in conjunction with bulk insulation, so heat retention occurs in combination with moisture prevention.
Reflective insulation loses its performance if it becomes tarnished. It also needs to face a still airspace, such as an under floor space.
R values for reflective insulation can start from R 0.6, depending on air gaps and placement.
Other insulation materials
Pumice is a naturally occurring material that has been used for floor insulation under concrete slabs.
Glass sheet (for windows) and glass blocks have good noise minimisation and insulation properties. Glass options are discussed in glazing> Design >> Glazing -->.
Polyethylene pipework insulation is used to clad pipes to prevent freezing.
More information
From Smarter Homes
From ConsumerBuild
From consumer.org.nz
Note: You may have to be a subscriber to access some of this content.
From other sites
The Energywise website has web pages on insulation and insulation design.
You can buy New Zealand Standards relating to insulation from the Standards New Zealand website. In particular, see AS/NZS 4859.1:2002 Materials for the thermal insulation of buildings and NZS4246:2006 Energy efficiency- installing insulation in residential buildings.
The Energy Efficiency and Conservation Authority’s energywise website has information on insulating your home including tips on installation, and case studies on the benefits of insulation.
Insulation case studies can also be found on the residential section of the Energy Efficiency and Conservation Authority’s main website.
Designing Comfortable Homes is a booklet about energy-efficient design, produced by EECA and the Cement and Concrete Association of New Zealand (CCANZ). A summary of the booklet can be downloaded for free and the full booklet can be purchased from the CCANZ website.
You can buy publications relating to building materials from the BRANZ Ltd website (click on the link for the online bookshop).
