Natural insulation materials: which is best?

Materials World magazine
,
1 Feb 2014

Man-made insulation materials often come with a heavy environmental cost. Rachel Lawler evaluates some natural alternatives.

In recent years there has been increased focus on insulating buildings, both commercial and residential, as a way of reducing carbon emissions and lowering energy bills. But the production processes of some man-made insulation materials come with heavy environmental costs, and the negative effects of toxic by-products produced in manufacturing and energy-intensive processes can counteract some of the benefits of using insulation. So, how do natural materials compare?

Some of the most popular natural alternatives include hemp fibre, flax, wool – but each has its pros and cons. As such, deciding which material is best overall depends on what you are trying to achieve. While a better insulated building will require less energy to heat, some homeowners may have additional concerns about the use of virgin materials and would prefer to use a recycled material to insulate their homes. Others are more troubled by the use of harmful chemicals and may look to materials that don’t require such treatments.

While all insulation materials will reduce energy consumption and heating bills, the materials selected will determine the overall environmental benefits of these improvements. Here we evaluate the energy credentials of some the most popular natural alternatives.

Cellulose fibre:  

Pros

  • Made from recycled newspapers that would otherwise go to waste.


Cons 

  • needs to be treated with flame retardant chemicals
  • thermal conductivity: 0.038–0.040W/mK
  • energy use: 4.9MJ/kg
  • insulation thickness: 150–190mm

 

 

Hemp fibre:

Pros

  • Hemp is a carbon negative material – every one tonne produced traps two tonnes of CO2, keeping it out of the atmosphere.



Cons

  • use of fertilisers and pesticides in crop production
  • thermal conductivity: 0.38–0.040W/mK
  • energy use: 33MJ/kg
  • insulation thickness: 165mm
  • insulation thickness: 150–190mm


Cork

Pros

  • Flame retardant and resistant to moisture and varying temperatures, cork is sourced from forest trees without permanently damaging their growth.


Cons 

  • cork dust can cause health problems for industry workers
  • thermal conductivity: 0.038–0.50W/mK
  • energy use: 1.38MJ/kg
  • insulation thickness: 240mm


Flax

 

Pros

  • Flax for insulation is a by-product of the linen industry and is both recyclable and compostable.


Cons 

  • flax is usually imported, increasing carbon costs
  • thermal conductivity: 0.038–0.040W/mK
  • energy use: 30MJ/kg
  • insulation thickness: 230mm


Sheep’s wool

Pros

  • Sheep’s wool can absorb and release moisture from the air, making it breathable and providing some ventilation.


Cons

  • possible use of pesticides and biocides in production
  • flame retardant
  • thermal conductivity: 0.034–0.054W/mK
  • energy use: 20.9 MJ/kg
  • insulation thickness: 150–215mm


Thermal conductivity
This measures how easily heat travels through each material, independent of thickness – the lower the number, the better the thermal performance.

Energy use
This number represents the total amount of energy consumed in the life cycle of a product, including raw materials extraction and manufacturing.