Among natural thermal insulators which have good biological characteristics there are wood fiber, cork, cellulose fiber, coconut fiber and natural wool. These materials are an alternative to synthetic insulation used in construction such as polystyrene and polyurethane.
THE natural thermal insulation materials they have two characteristics in common. The first is to be breathable, which makes them suitable for solutions where in addition to the insulating performance, thermohygrometric comfort counts. The second is a generally lower consumption of energy in production (compared to synthetics) which makes them ecological.
Of course: just being natural is not enough to make insulating materials good. Do you know asbestos? Well, since it is rock dust, asbestos is also a natural material, and moreover an excellent insulator. As we say in the first line, the difference between good and bad is the biological characteristics. And these are the ones who reject asbestos and the like.
Some natural thermal insulators with good biological characteristics
Wood fiber panels. They have a conductivity coefficient λ around 0.050 and very low energy consumption in production. The ecological balance is excellent and they are recyclable as fuel. It is important, however, that these are panels produced with uncontaminated ground wood waste and reduced to wood wool. Only the panels that use the lignin contained in the wood itself for the binding process are truly natural, without the addition of glues.
Natural blond cork in panels or granules. The conductivity coefficient λ ranges from 0.030 for high density panels to 0.100 for bulk granules. The energy consumption in production is also very low in this case. Natural blond cork is a renewable material from the bark of the cork oak (which regenerates). It can be defined as 'natural blond' only if it is not cooked (cooking in the oven lowers its stability and releases pollutants), and if the aggregation of the panels is given by the suberin contained in the cork itself without the addition of artificial binders.
Cellulose fiber flakes. They have a conductivity coefficient λ is about 0.032 and the energy consumption in production is very low. The flakes are made with recycled newspaper and subsequently treated with boron salts (not with anything else) in a fireproof and pesticide function.
Coir panels and mats. This material has an average λ of about 0.045 and low energy consumption in production (excluding transport). Coir is obtained from the mesocarp of the coconut, the thick fibrous layer that covers the shell. It is resistant, immortal, and is not afraid of humidity and insects. It is very thermal insulating, but also quite expensive.
Felts and natural wool flakes. They have a conductivity coefficient of 0.033 and modest energy consumption in production. Animal wool is used loose for filling cavities and in felts as underfloor insulation. It is very heat-insulating, but again it is a rather expensive solution. It is attackable by parasites (it is treated and it is necessary to inform us with what) and not recommended for allergic people.