Cellulose vs. hemp vs. cork: which eco insulation is best for UK homes?
Worried about your home’s environmental impact? Insulating your home is a good way to cut your carbon emissions, but have you considered the sustainability of the materials used to insulate it?
The good news is that there is a growing range of eco-friendly insulation products to keep your home warm (or cool when required) in a more sustainable way.
Eco-friendly insulation falls into two broad categories:
- Natural insulation. This uses materials derived from plants. It has a smaller carbon footprint than manufactured materials and is naturally renewable, biodegradable and recyclable. Some types are also naturally resistant to water, mould and pests, so require fewer chemical treatments
- Recycled insulation. This makes use of existing manmade materials like cellulose (paper) and plastics to avoid virgin materials being used or the recycled materials ending up prematurely in landfill.
These eco-friendly materials can be manufactured into a range of products, allowing you to insulate everything from both cavity and sold walls to your loft, floor and any other gaps that might need filling.
Why choose eco-friendly insulation?
The primary reasons for choosing eco-friendly insulation are environmental, including:
- Produced from naturally grown or recyclable materials, so require less energy to produce
- Plant-based materials are biodegradable, renewable and recyclable
- Some materials capture more carbon when grown than that required to turn them into insulation, helping to cut emissions
- Few (if any) chemical or non-biodegradable additives
- Many types are relatively easy to work with and can be fitted by an experienced DIYer.
The good news is that you don’t have to compromise on the effectiveness of your insulation by choosing an eco-friendly product. Many offer similar thermal performance to traditional insulation materials like rock and glass wool*.
And while most eco-friendly insulation costs more than conventional insulation, prices vary widely, enabling you to choose a more environmentally friendly option without breaking your budget.
*Note: most thermal conductivity ratings below are taken from A Comprehensive Comparison of Insulation Materials for Timber Building Systems, a study published in May 2025.
Cellulose insulation
Cellulose insulation is made from a mix of recycled newspaper (around 85%) and other organic compounds, shredded and pulverised into soft fibres. During this process, it’s usually treated with a combination of boric acid and ammonium sulphate, two non-toxic compounds that help make it flame-retardant and resistant to mould and pests.
In most cases, cellulose insulation is supplied in a loose-fill state but has also been manufactured in pellet form. It’s primarily used to insulate:
- Lofts: the fibres are poured directly into the space between joists to fill the space
- Timber-framed walls: the fibres are blown into timber-frame cavities using air pressure before the frames are boarded up. In most cases, the insulation is slightly dampened (it can absorb up to 30% of its own body weight in water without affecting its insulation performance) before being ‘damp-blown’ into the cavity
- Solid floors: pellets can be installed in some floors with a sub-floor fitted.
In terms of insulation performance, cellulose insulation has a thermal conductivity of 0.037-0.042 W/m.K, which is similar to that of rock and glass wool.
Pros and cons of cellulose insulation
Pros
One of the most competitively priced sources of eco-insulation (around £9-£12/m2)
Treated with non-toxic chemicals to make fire-retardant and pest-proof
Excellent heat resistance properties, on par with other major insulation types
Diverts waste from landfill and doesn’t require additional resources to grow or nurture plants and animals
Fully biodegradable
Easy to install as loft insulation, suitable for DIYers
Cons
Still comparatively expensive - up to twice that of mineral wool or rigid foam
Susceptible to damp, fire and pests if not treated and installed correctly
Uses more energy to make it fire-retardant, so less ‘green’ than other options
Can compact over time, reducing its insulating abilities
Hemp insulation
Hemp is a fast-growing plant used for a variety of purposes, including insulation. It’s an excellent choice for eco-conscious builders because it’s one of the most sustainable and renewable materials available, and it’s naturally breathable, helping regulate moisture in older homes.
Once harvested, the plant is bundled and left outdoors before being subjected to a mechanical process that separates the outer fibres from the woody core. These long, strong strands of fibre are then used to create insulation; they also serve as a fibre component in other eco-friendly building materials, such as hempcrete and hemp lime plaster.
Hemp wool is used to create insulation rolls, batts and boards, all of which can be cut to size and are made available in a range of thicknesses. You can expect to pay around £12-£27/m².
Batts are remarkably resilient. For example, they can be dried out and reused if completely saturated in water (say, as the result of a plumbing leak). They’re designed to fit easily between structural framing, such as timber frames and joists, making them ideal for use in lofts, between floor joists, around windows and doors and on solid walls.
In terms of insulation performance, hemp’s thermal conductivity rating varies more widely than other materials: 0.038-0.060 W/m.K, partly due to its high levels of water absorption, which makes it less suitable for use in areas prone to damp. But when used appropriately and installed correctly, its performance is on a par with non-eco materials.
Pros and cons of hemp insulation
Pros
Biodegradable, lightweight and naturally resistant to mould, bacteria and pests
Fast-growing, requires few resources
Better at carbon capture and storage than trees
Naturally breathable to help regulate moisture and prevent condensation buildup
Good sound absorption qualities
Decent thermal properties that aren’t affected when the insulation is compressed
Can be used as an insulating layer in other building materials like hempcrete and hemp lime plaster
Cons
Not widely used in the UK, so more expensive than non-eco materials
Boards require specialist tools (and expertise)
Thermal conductivity ratings vary more widely than other materials
Not suitable for use in potentially damp environments without a vapour barrier, such as cellars and basements
May require additional treatment to make it fire-resistant.
Cork insulation
Cork insulation is made from various parts of cork trees, from bark that can be harvested without killing the whole tree to waste products left over from bottle stopper production.
The cork is transformed into various forms of insulation for multiple uses:
- Walls, floors and roofs: choose panels or boards; use thinner rolls in restricted spaces or as underlay for floors
- Gaps in cavity walls, ceilings and floors: use cork granules
- Insulative surface layers: apply cork insulation spray.
Boards are produced in as little as 20 minutes. By-products from cork stopper production, such as the tree’s branches, are ground into granules that are placed in an autoclave and subjected to heat and pressure treatment to extract the resin, which naturally binds the cork into a solid piece. From here, blocks are cut to various thicknesses, primarily for insulation.
Cork is a good thermal insulator thanks to its honeycomb-like structure, which traps pockets of air that help reduce heat loss. As a result, its thermal conductivity rating( 0.037-0.043 W/m.K) puts it on par with both rock and glass wool insulation. Cork insulation for walls is also sought after thanks to its water-repellent qualities.
Pros and cons of cork insulation
Pros
Fast-growing and naturally occurring
Some techniques allow it to be harvested without killing the tree
Naturally water-resistant, so can be used as part of external solid wall insulation without additional treatment
Breathable, which helps regulate humidity levels and prevent condensation
Able to absorb up to 70% of sound
Effective thermal insulator (better than rock wool insulation)
Non-toxic and hypoallergenic
More durable than other materials.
Cons
Not widely produced in the UK, which makes it more expensive (up to ten times the price of equivalent mineral wool products)
Check fire-resistant properties - while it doesn’t burn quickly like other wood, it may still require treatment
May attract rodents and pests if not treated
Not all cork is equally sustainable - some types of cork for insulation use synthetic bonding agents (agglomerated cork) rather than natural resin (expanded cork)
Question marks over the overall sustainability of cork
Other eco options to consider
Hemp, cork and cellulose aren’t the only eco-friendly forms of insulation available. Here are three other types to consider.
Wool
Wool is harvested from the back of sheep through regular shearing. It’s 100% natural and biodegradable and is commonly produced as batts and sheets for applications similar to those of mineral wool insulation, including lofts, wall cavities and between joists on suspended timber floors.
Pros of using wool include:
- Renewable
- Extremely breathable, making it very efficient at both absorbing and releasing moisture
- Simple to install
- Naturally fire-resistant
- Good thermal conductivity (0.038 to 0.054 W/m.K)
- Made from keratin, which can neutralise some indoor air pollutants (e.g., formaldehyde)
There are some drawbacks you should consider before choosing wool, such as:
- One of the most expensive options at around £18-25/m2)
- Not as eco-friendly as plant-based solutions due to the environmental impact of rearing sheep
- Requires chemical treatments to prevent pests
- Thermal conductivity worsens as the material is more densely packed - aim for no more than 40 kg/m3.
Sheep’s wool is a perfect choice for those looking to insulate older properties, as it’s both breathable and mould-resistant, making it a good choice for insulating internal solid walls and timber frames.
Recycled PET
Recycled plastic insulation is insulation manufactured from PET plastic recovered during the recycling process. The plastic is then shredded and ground into flakes that are dried before being melted and formed into thin plastic pellets. Finally, the pellets are mixed with mineral fillers and chemicals to enhance insulation properties, then pressed into batts or rolls for use in lofts or as loose-fill insulation in cavities.
Plastic insulation is a good thermal insulator because not only is it non-conductive, it’s also filled with tiny pockets of air. The thermal performance of recycled plastic insulation rolls has been measured at 0.040 W/m K.
Reasons to choose PET-based insulation include:
- Extremely affordable - just £3-£11/m2
- Helps divert waste from landfill
- Versatile - comes in many forms, including loose-fill, rolls and rigid board
- Naturally moisture-resistant, which prevents the buildup of condensation and mould
- Easy to cut to fit, so suitable for DIY enthusiasts in some forms
Reasons why it may not be the best choice for your home:
- Thermal performance not as good as other eco-alternatives
- Not as green as naturally grown or plant-based solutions
PET insulation is an affordable choice for those who want an eco-friendlier option than traditional materials and may be preferable to cellulose because it doesn’t easily compact and doesn't require treatments against fire or moisture.
Low-impact foams
These foams are made from a combination of non-toxic, renewable liquid materials. Their primary use is to create airtight seals to minimise air leakage (and so improve thermal performance), so are best used in conjunction with other insulating materials to fill in gaps and provide a moisture barrier where needed.
However, foams come with a high cost (as much as £20-£50/m2), require professional installation and can be challenging to remove, making future repairs or renovations more difficult. It’s also important to do your research, as not all foams come from renewable or recycled materials.
How to choose the right insulation
There’s no one-size-fits-all approach to insulating your home, but broadly speaking, the more you’re willing to pay, the more sustainable the insulation you can buy.
If that’s not your primary motivation, the following factors may help steer you towards a particular type:
- Install eco-friendly insulation without the high cost: choose insulation made from recycled materials, whether paper (cellulose) or plastic (PET)
- Choose insulation with greater resistance to moisture: cork offers the best water-resistant properties for damper climates
- Choose a breathable insulator for an older home without sacrificing its charm: both sheep’s wool and hemp can regulate humidity while offering strong thermal performance
- Match the performance of traditional materials like rock and glass wool: again, cork rivals the insulating properties of non-eco materials.
FAQs
Which insulation materials are most environmentally friendly?
Natural fibres score highly on the eco-friendly scale because they’re biodegradable and recyclable. But if you’re looking for the most environmentally friendly material to use, then hemp scores highly because it grows quickly, requires little water and is perfect for growing on low-quality land where its root structure allows it to not only capture lots of carbon from the atmosphere, but transfer it into the soil, helping to regenerate it and store it long-term.
What is the best natural material for insulation?
This depends on your budget and what you’re trying to insulate. Cellulose insulation offers an affordable way to insulate your home using natural materials, but for older homes, both hemp and cork offer a more breathable insulating layer to meet the need to regulate its humidity. If the home suffers from damp or is in a wet environment, then cork offers the best water-resistant features.
What are the disadvantages of hemp insulation?
Potential drawbacks of choosing hemp concern its relatively high price (in part due to a lack of availability), variable thermal performance and its lack of suitability for use in areas susceptible to damp.
Is cork insulation effective for walls?
Yes, cork is an excellent choice for insulating solid walls thanks to its combination of water resistance and breathability, which helps manage humidity inside the home. Its ability to repel water also makes it suitable for use in external wall insulation without additional treatment.
What is the greenest insulation for UK homes?
Hemp is the greenest insulation material for UK homes. Environmental benefits of using hemp include:
- Hemp can be grown on poor-quality land and requires little water or pesticides
- Hemp absorbs CO2 at a faster rate than forests while it’s growing
- Carbon isn’t simply stored in the plant’s stem, but also transferred to the soil via its long tap roots. This helps sequester carbon in long-term storage, plus regenerates the soil naturally.
