Insulation materials serve a critical, if underappreciated, role in our homes. They reduce heat loss, keeping our spaces livable and lowering energy bills. The result is improved sustainability in our homes and other buildings, making insulation a critical part of the movement towards Net Zero.
However, traditional insulation materials carry other environmental costs, such as petrochemical sources and high-energy manufacturing methods. Additionally, options such as glass or mineral fibre cause irritation to the eyes, skin, and lungs, and are potentially carcinogenic as the body struggles to remove these persistent dust fibres. Workers installing these materials require protective equipment to stay safe. To really improve the greenness of our homes, insulation should be made from sustainable, safe materials that use little energy in manufacture and can be recycled or composted once removed.
Sustainable insulation materials
There are various forms of sustainable insulation available from renewable or recycled sources including both animal- and plant-derived natural fibres, bulk plant mass, and recycled textiles/plastics. Some of the options are:
- Sheep’s wool
- Wood wool
- Hemp
- Cellulose
- Straw bale
- Cork
Usually, natural insulation materials are treated with low-hazard chemicals such as borate to act as a flame retardant and protect against mould.
Choosing a sustainable insulation material
As usual with sustainable materials, there’s no one “best” product – the right choice depends on your specific needs. We’ve summarised some of the pros and cons of the best-known green insulation options below.
Sheep’s wool
Sheep’s wool evolved to keep sheep warm in the winter, making it a fabulous natural insulator with high thermal properties. It works by forming many small pockets of air that retain heat. It can be fairly fire resistant, usually falling in Fire Class B2-E, indicating that it will char in fire. The ecological benefits of sheep’s wool are that it comes from a renewable source and often has end-of-life options besides landfill, including recycling or composting. It is also vapour-permeable and so allows building materials to breathe and regulate moisture.
Another advantage is the potential for air purification. Sheep’s wool naturally absorbs some harmful VOCs such as formaldehyde, which may be found in the home, possibly creating a healthier indoor environment.
One disadvantage of wool insulation is that it is vulnerable to insects such as moths, therefore requires chemical treatment to last, but this is quite common in natural products. Sheep’s wool can also come up quite expensive compared to other materials at around £17.50 to £22 per square metre.
Wood Fibre
Wood fibre is another renewable insulation material that is non-irritating, provides a high heat storage capacity and reportedly good acoustic insulation. Other advantages include the fact that it is vapour-permeable and damp-proof. Sources of this material are available from sustainably managed forests, and it can be made from spruce, which is native to Northern Europe and relatively fast-growing. This means the energy used in transportation for a UK or Northern European market is relatively low, reducing carbon emissions.
Like sheep’s wool, wood fibre can be unfortunately expensive at £16.50 to £20 per square metre. It is also not as readily available as other materials at the current time.
Hemp
Hemp is a strong, fast-growing, plant-based insulation material. A benefit of growing hemp for industrial use is that it is a robust plant that does not require significant quantities of pesticides. It has low embodied energy and provides good thermal and acoustic insulation.
Hemp insulation is compostable after use. It is a non-irritating substance available as both blankets and boards. Due to their structure, manufactured hemp panels interconnect easily and do not require additional thermal bridges.
Hemp is breathable and moisture-regulating, although not suitable for a damp environment such as a bathroom. Despite this, it can theoretically be removed for drying and then reused. As with other bio-based materials, it does require chemical treatment to ensure fireproofing (class B2) and mould resistance. Pricing comes in at £15 to 20 per square metre.
Cellulose
Cellulose insulation is relatively cheap, similar in value to rock wool. Its ecological benefits are that it is made from recycled paper, such as newspapers, which would otherwise go to landfill to decompose and give off CO2. Loose fill and densely packed versions are available, and the right choice will depend on the build requirements. Cellulose is breathable, but not suitable for long-term use in damp environments. At costs of £12 to 18 per square metre, it is relatively inexpensive compared to other ecological insulation.
Cellulose insulation is blown in and requires a blowing machine so may require professional installation. It is typically treated for fire resistance with a low hazard chemical such as borax, giving it a Class 1 fire rating.
Straw bale
Straw bale is another plant-based insulation material that is also used as a construction material. It has the ecological advantage of coming from an agricultural by-product and so is not a competitor for food land use. Advantages include that it is a lightweight material that is widely available and locally sourced. It is fairly simple to use so can be installed in DIY and self-build projects. Straw bale does not require thermal bridging and provides good airtightness but is still vapour permeable. Costs are in the range of £17 to 22 per square metre.
The limitations of straw bale are that its properties can be inconsistent, coming from multiple agricultural sources. It is not as resilient in damp environments as some other types of insulation.
Cork
Comes from the bark of the cork oak tree, which is harvested carefully without needing to cut down the tree. It is manufactured in the form of granules or boards and is easy to install. No irritation or dust is encountered with cork and it is suitable for damp environments. Furthermore, cork provides good acoustic insulation and is and has good fire-protection ability (fire class B2, meaning ‘extremely fireproof’). Both durable and highly insulating, cork is also produced in a clean way with no chemicals or artificial additives required in the production process.
Pricing comes in at £17 to 22 per square metre. The disadvantages of cork are that it needs to be imported from Portugal or North Africa, where the tree is native. It also has quite a long gestation time as the tree must mature for about 9 years before harvesting the bark and it must be allowed to regrow, so there will always be limited supplies.
Conclusion
The role of insulation materials in sustainable building practices by cutting energy use, costs and, ultimately, carbon emissions is well understood. It remains now to improve on the quality and sources of these materials so that renewable insulation takes the larger share of the market. There will need to be a willingness to take on higher costs at the beginning while production processes become better established. However, it is likely that rising oil costs and legislational pressures will drive the market from the other end as well. As with all efforts to improve sustainability, this should be done with a holistic approach to implement green solutions while maintaining practicality at scale.