Natural Insulation – What do you need to know?
Effectively insulating our living spaces is increasingly vital for keeping energy costs down, improving living conditions and modernizing outdated dwellings.
Buildings are a central part of our daily lives, and we spend a large part of our days in them.
“In its different forms – homes, work places, schools, hospitals, libraries or other public buildings – the built environment is, however, the single largest energy consumer in the EU. And one of the largest carbon dioxide emitters. Collectively, buildings in the EU are responsible for 40% of our energy consumption and 36% of greenhouse gas emissions, which mainly stem from construction, usage, renovation and demolition.
Improving energy efficiency in buildings therefore has a key role to play in achieving the ambitious goal of carbon-neutrality by 2050, set out in the European Green Deal. Today, roughly 75% of the EU building stock is energy inefficient. This means that a large part of the energy used goes to waste.” 
Certain strategies to reduce these carbon emissions are focused in improving building design and its thermal insulation performance, for both new and old constructions, looking to enhance heating efficiency and ensure comfort within the building without wasting our valuable resources.
Insulation has the greatest potential for reducing CO2 emissions. The energy conserved through insulation can compensate for the energy used during the manufacturing process of it while CO2 conserved by natural insulation can also outweigh the CO2 emissions created during its manufacturing process. This is why the transition to natural insulation materials is key to achieve energy efficiency and net zero buildings.
But, what is a natural insulator and which are the options available?
And which are the factors to take into account when choosing one?
We came up with this detailed guide to help you choose the best natural insulation for your needs, plus a comparative spreadsheet you will find at the end!
Natural Insulation Materials
As a definition, “natural insulation is made from natural-occurring sources with thermal properties” . Generally, these come from plant-based sources (different plant fibers) and even animal-based, mostly sheep’s wool (usually reused). Within this we are also going to take into account recycled sources such as textiles waste streams (cotton) or paper (cellulose) and more experimental ones (mycelium).
It is true that some conventional insulators, such as rockwool, are also made from stone-based natural raw materials, but these are largely not considered a form of natural insulation, because of the huge amount of energy required in the manufacturing and recycling process.
Originates from the hemp plant, which possess strong woody fibers that are very durable and have excellent insulative properties. Hemp offers fantastic environmental advantages, it is renewable and biodegradable and requires really low energy and maintenance to cultivate. It can grow on almost every soil impressively fast, with a 100 day full growth span all year round. It is also non- toxic, requires no pesticides or insecticides and consumes very little water. It sequesters more carbon than it consumes during construction; a process that continues during its installation.
Straw bales and straw-clay blocks had been used to build houses for centuries. Back in the day it was done by stacking bale walls and covering them in mud, but nowadays prefabricated straw insulation and building panels are beginning to appear on the market.
Straw bale walls are made out of the remains of grain harvest, so they come from a recycled source and act as a carbon storage reducing the environmental impact. Another remarkable property of this material is that it is a good sound insulator.
The flax used in insulation is a secondary product from the linen industry, it is derived for the stalk of the linseed plant, which has lower economic value, it is not strictly waste, but it’s a way of using this remaining raw matter.
Can be made from any type of cellular plant source. It is mostly made from recycled newspaper, but it can also include other recycled paper, cardboard, office paper and other paper products. containing over 90% of post consumer recycled material. It is very popular and has been in the market for many years.
Versatile and durable material. Cork insulation is made from cork bark that can be harvested every nine years without damaging the tree, which has a 150-250 years life.
This practice has even been proven as healthy for the tree and the material obtained it’s 100% natural and renewable. Meanwhile cork forests protect from wind erosion and act as fire barriers stabilizing the soil, cork is also a natural fire protector.
It is known as wood fiber insulation because is made from the soft wood waste material like forestry thinnings and saw mill residue. It came as the result of wood processing industries willing to reduce and make something out of their waste.
Wool’s goal is to keep sheep warm and it does just as good a job for them as it does for us. Their fibers are crimped, trapping air, which is an excellent insulator.
Wool insulation is made nearly entirely from sheep’s wool, usually reused, this material is sustainably produced and biodegradable. Wool goods can be completely recycled obtaining high quality raw wool again.
The cotton that is used in insulation is sourced mainly from recycled pre-consumer clothing, mostly denim, and also some agricultural cotton scraps.
This is a smart solution for the aim of reducing landfill waste. The fashion industry is a massive waste stream producer so finding ways to recycle and reuse old garments is essential and turning your old jeans and other clothes into insulation is one way of doing it.
Grass is an abundant product that grows and reconstituted naturally all over the world. We can transform grass from waste to useful product, taking profit from the mowed grass by incorporating many local ecosystems and then manufacturing insulation panels to build efficient buildings and homes with it.
Mycelium is a part of a mushroom that consists of a network of thin filaments called hyphae, similar to a root system it collects nutrients to feed the fungus. This natural phenomenon has become an innovative material with the potential of taking over the market and opening its way in the construction sector.
Mycelium based objects are a relatively new occurrence (the oldest known blocks are 20-30 years old, developed by Philip Ross). Recently some companies have been betting on it and we are starting to see the first manufactured mycelium based products, between which we can find insulation panels due to the impressive thermal and acoustic properties of this material.
Hyphae spreads through the substrate the fungus is growing in. To make these panels they are using commercial and agricultural by-products as a substrate for the mycelium to grow, creating a product that basically manufactures itself and taking advantage of leftovers that would otherwise go to landfill.
There is a lot of enthusiasm behind these and we should see more and more mycelium derivatives and insulation products in the coming future.
We have other articles and an online course explaining how this works and how to build your own, check them out!
When comparing insulations we should take into account some matters.
Concerning the performance quality of the material, we need to compare the following.
Measures the thermal conductivity of a material which indicates the capacity of a material to conduct or transfer heat (energy) through its mass. This is measured in watts per meter-kelvin (W/(m⋅K)) (SI).
When trying to identify the better thermal performance of an insulation the lower thermal conductivity, the better.
Measures thermal resistance, the ability of a material to resist heat transfer.
This figure connects thermal conductivity of a material to its width so it is expressed in resistance per unit area (m2·K/W). A material with high R-value means it has good insulation properties.
R-value refers to the material and its thickness while K-value deals with just the material, so it can be used to compare raw materials instead of being a qualifier of the insulation product.
There’s something else to consider after the insulation materials to account for the fact that materials react in a different way when energy is added to them. Thermal inertia is the “property of a material that expresses the degree of slowness with which its temperature reaches that of the environment” . This means that the material can store energy and regulate the amount it releases.
We measure this with the specific heat capacity, which specifies the amount of heat required to raise the temperature of 1 kg of material by 1°C (K), a material with a large specific heat will warm slower than a material with low specific heat.
This will ensure a comfortable space not only during colder seasons, but also during heat waves so these characteristics are especially important in summer or hotter climates in order to prevent overheating.
Natural materials outperform synthetic ones on this. Heavier materials can store more energy, meaning they warm up slower. Simple insulation materials (mineral wool, foamed chemical products…) have lower thermal inertia because they are very light, so they warm up quickly. In opposition bio-based insulating materials are heavier so they perform better at redistributing the energy when needed.
Is the time required for the heat to penetrate through a certain material.
During the day, the outer temperature fluctuates between a maximum and a minimum value. What happens is that the interior temperature tries to mirror the exterior temperature and it does after a certain time, this time lag is what the Phase Shift expresses (hours).
For instance a glass wool has a low thermal phase shift, indeed heat penetrates in 3-4 hours. To the contrary cellulose wadding has a long thermal phase shift of 11 hours. 
Knowing all of this, think about it this way – a material with high thermal inertia can conduct heat away from its surface quickly (high thermal conductivity), can absorb more heat with less temperature gain (high specific heat), and has a lot of mass/unit volume (high density). With more mass in which to store heat energy, a relatively slow temperature rise occurs. 
If you want to make a real environmentally friendly decision we should also be aware of the CO2 balance.
Insulation itself is going to save energy by balancing the amount conserved throughout the performance life of the insulation with the energy necessary to produce the material is key.
Buildings, or what we name as the built environment, generate 40% of annual global CO2 emissions.
27% of those are building operational emissions, wich is the energy needed to heat, cool and power them. Building and infrastructure materials and construction are responsible for an additional 13% annually.
This 13% of CO₂ emissions is what is typically referred to as embodied carbon of a material. To tackle this any carbon emission created during the extraction, manufacturing, transport and the construction and end of life are taken into account.
We can bring this number down by making the right insulation choice!
A judicious selection of building materials can not only reduce the amount of carbon dioxide released by this sector, we can achieve a zero carbon or even carbon negative construction. But, how is this even possible?
During their growth, thanks to photosynthesis, plants capture CO2 from the atmosphere and store it. After harvesting this gas remains inside them for all their use life including recycling, it will be out of the carbon cycle for several decades, as long as it is not decayed or burnt. This amount of stored carbon in material is known as sequestered carbon. In many plant based materials, this sequestered carbon can be significantly higher than carbon needed to produce it, that’s why it is something to consider when determining the global warming potential of a material.
If we want to make a conscious choice we should also be taking into account the manufacturing process and the bonding and treatment substances added to manufacture product.
Non-natural insulation comes from a combination of raw materials, usually unused before, which are bonded with chemicals or melted at extremely high temperatures, amounts of energy to be produced.
Natural insulation also needs energy to be produced, but it’s significantly lower, comes from renewable sources and many of them, like straw bales, are even waste from other industries or recycled materials. Natural materials sometimes are also bonded to better their performance, but in smaller quantities and the manufacture process is significantly simpler.
Natural insulation can be naturally protected from external factors like insects or moisture, humidity and fire but, also because of its nature, it may also need some additional treatment. We should take a close look at the composition to make sure there are no extra glues or binders added and that, in case some treatment is needed, these substances are naturally sourced as well.
Sources and End of life.
It is very important to know where the material comes from and what we do with it at the end of its life.
Plant based insulations come from renewable sources usually with harvest streams or other industries leftovers, while other sustainable options come from recycled products with origin in natural raw material.
The essence of natural insulations is that they are degradable at the end of their lifecycle, in the worst case even if they end up going to landfill, they will break down in a relatively short period of time and benefit the soil.
Some synthetic insulation can also be recyclable, but the problem is that the amount being recycled is still a really small proportion. Most of it ends up in landfill or gets burned, adding more waste to the plastic pollution problem.
Application and Format.
Other than by its source we can classify insulation by the format they come in or the way it looks as a manufactured product. This characteristic is anyway mostly linked to the nature of the material of origin.
We will have to take this into account depending on which areas we are going to insulate, and mostly If we are going to install the insulation ourselves.
There’s a classification of the different insulation types and their usual applications. When it comes to natural materials we can find:
Solid boards. Because of its rigidity it can be attached to surfaces and will not require an integral support. We usually find them as sarking boards systems with or without OSB support on top of the rafters. Wood fiber and cork boards are the most common examples.
Semi-Rigid or flexible blanket insulation. It is the most recognizable and commonly used, we can find it in batt and rolls. It is introduced between frames, studs, joists, and beams and it can be used in both vertical (unfinished walls) and horizontal (floors and ceilings) applications. It comes in standardized sizes but can be cut to fit the space. These do require vertical or horizontal support.
Natural sources to make this kind of insulation are mostly any kind of plant fibers.
In general, natural insulation materials are still more expensive than conventional ones. But if we look at the price of the raw natural material we see that usually it is really low due to the fact that most of them are harvest or waste streams.
Even though the monetary cost is a bit higher if we balance the global cost is much lower. As we said, natural insulation is way less polluting, uses renewable resources and is environmentally friendly.
Its application is also safer and it improves breathability, due to the hygroscopic nature of natural fibers, the insulation is able to absorb, store and release moisture, naturally controlling condensation levels within the building and improving internal air quality, so it also pays off for our health .
For insulation to last, it must be resistant to external aggression (rodents, insects or humidity) but also not settle over time (which is the case with cotton wool or linen, for example). Life-cycle assessment must take into account service life and durability for each material of the system. The higher durability of natural insulating materials and less performance loss over time allows for the execution of less maintenance interventions.
All of this will save lots of energy during manufacture and during the operative life of the building, this makes natural insulation more cost-effective, because energy efficiency also translates to saving money.
Knowing now the types of natural insolations and what to take into account when comparing them we have gathered all the information into this comparative table.
Note that different manufacturers’ techniques and procedures result in different characteristics of the insulation. In order to be able to accurately compare information, we are mainly looking at the material itself, not a market product, but which characteristics should then be directly related to it. So note that the CO2 footprint and water usage, specific heat capacity and price is sourced from the software Granta Edupack built environment database, referring to the general material, while for the thermal conductivity and CO2 balance facts we looked up representative market offers.
 M. Fan, F. Fu, in Advanced High Strength Natural Fibre Composites in Construction, 2017.