Natural Insulation

Insulation in buildings is important. It’s like your duvet – it helps to regulate the temperature in your home and keep it constant. It helps to keep it warm in winter, cooler in summer as well as helping with noise pollution. Some types have also been in the press with the ongoing Grenfell enquiry for their combustability. So what are different types of insulation? I’m not going to look at every option – just the most common and some more natural alternatives.




As a general rule, newer houses are relatively well insulated (although not necessarily as insulated as they should or could be in my opinion!) and older houses have the least insulation. The majority of the heat will be lost through the walls. The next most through the roof, then windows and doors, and then floor.




There are many different types of insulation. Rigid insulation is generally better for walls and pitched roofs, while flexible insulation is good for laying over your ceiling joists in your loft.


Mineral wool insulation is one of the most common types you’ll find at the diy stores. It’s usually relatively cheap, it doesn’t burn in a fire, often contains recycled or waste products and is recyclable to a certain extent itself. It can, however, be irritating to your skin and lungs if you breath the fibres in – so you need gloves, to cover your arms, legs and eyes and wear a mask. It can also sink and sag over time, meaning it becomes less effective at keeping the heat in.




There are some natural alternatives.


          Woodfibre board (top two samples in the picture below)


          Recycled cotton from clothing (you can often see the denim strips in the insulation – the blue sample in the picture below)


          Sheeps wool (grey fluffy sample below)


          Cork (dark / black sample below)


          Recycled plastic bottles




Wood fibre board is often used as external wall insulation, followed by a render top coat. It’s not manufactured in the UK as far as I know, so it’s imported. It’s good in the fact that is’s fairly OK to use with any building type, but timber buildings is where it’s really useful. It’s at the lower end of the natural insulation price scale, but it’s not as good an insulator as other products, so you need a lot more thickness for the same level of insulation.




Cotton is natural, renewable, recycled and doesn’t cause breathing problems or irritate the skin. Brilliant! Why aren’t we using it more often? Because it’s really expensive. Here’s a less blue version where you can see the fibres:




Sheep’s wool – We in the UK burn a lot of fleeces each year from animals whose coat isn’t suitable for clothing or other uses. Thermafleece are a UK supplier who work with UK farms to use the fleeces, and mix them with recycled polyester to make insulation. It doesn’t itch (although they recommend a dust mask in enclosed spaces), it’s difficult to burn, it’s great for acoustics and it’s bug proof. We used it at Cranbrook for the ceiling. It’s at the higher end of the natural insulation spectrum. It’s especially useful to insulate older homes that don’t have any existing insulation. It’s a great product. I don’t know why we don’t use it more.






Cork is a relatively common insulation in Europe. It’s a Portuguese sustainable crop. It’s water and damp resistant and easy to cut. It’s even been used to build an entire house




Recycled bottles. Think polyester duvet fillings and you’ve got the idea for recycled bottle insulation. It’s safe to handle and uses recycled products. You can lay it over your existing insulation too. I suppose it’s a good use of plastic bottles that would otherwise have been sent to land fill, but I don’t know if it kind of works against the issue of single use plastics. It’s a good option if you need to top up your existing insulation.




Hemp is an amazing product. It’s a fast growing, low impact crop that has many uses. Hemp seeds are a food source, as is hemp milk, hemp fibres can be used for clothes, the waste products can be used as a biofuel. Hemp can be made into paper, bioplastics (questionable), insulation and used as a building material.


The issue with hemp? The cannabis element, or at least the CBD element. You need a licence to grow it, and you need to inform the police, even if the hemp is a low THC crop.


But it does make really good insulation. And mixed with lime ( a cement alternative), it makes a wet mix insulated building product. It’s a bit more expensive than the frequently used building materials.




So often for insulation, the reason for not using more sustainable alternatives is the cost.