Properties and advantages

Cellulose has been used as an insulation material for more than 100 years. It was first used in North-America, but in recent decades has also become widely popular in Europe. In Finland it is the most popular blown loose wool. Here you can find a description of Werro Wool cellulose insulation and the reasons for it being an excellent insulation material.

Excellent thermal resistance

Werro Wool cellulose insulation has better insulating properties than competing materials. Insulating properties are measured with the thermal conductivity coefficient (lambda – λ). The thermal conductivity coefficient shows how much heat passes through a cubicmeter of material in one second while the difference of temperature on either side of the block of material is 1°C. The smaller this figure is the better the insulating properties of a given material. Werro Wool cellulose’s thermal conductivity coefficient (λ) is 0,0409 W/mK. This measurement was made by an independent laboratory in Denmark and its test protocols can be found here. This figure beats competing insulation materials (0.042 W/mK for blown fibreglass and 0.045 W/mK for blown stone wool respectively).

While lambda measures the heat conductivity of a particular materal, the U-value, or the thermal conductivity of an external barrier, deals with the entire structure. The U-value represents the heat loss through a unit of the structure’s surface area. The thermal resistance value R of a given material is used when calculating it. With the U-value in mind the designer of a building can decide which materials and in what quantity to use. 

Werro Wool’s excellent insulating properties result from it being made of waste paper that in turn is made up of cellulose fibres. These fibres have exactly the right porosity and contain lots of static air.

The blowing indicator or the wind resistance coefficient of Werro Wool also makes it better than its competing blown loose wools. It cuts down convection in the structure and thus contributes to better thermal resistance:

  • For an attic, inserted ceiling or floor with the density of material 30 kg/m3, respective indicator is 5 kPa s/m2
  • For a dry-mounted wall with the density of material 60 kg/m3, the respective indicator is 37 kPa s/m2
  • For an inclined ceiling with the density of material 45 kg/m3, the respective indicator is 10 kPa s/m2

Natural ventilation and moisture control

Werro Wool is great for its ability to absorb moisture and release it over time. Mineral insulating materials lack such capabilities. Its ability to ventilate itself means that Werro Wool needs no vapour barriers. The absence of vapour barriers means that the building ventilates better, has an improved thermal environment and there is no risk from water condensation. Ventilation and thermal environment are especially important in areas where radon (toxic gas emanating from earth’s crust, harmful for the human body) levels are higher than normal.

Werro Wool also keeps the structure’s humidity under control, which will cut down the number of cold bridges and extends the lifetime of the structure.

Allergy free

Because Werro Wool is made of a natural material (wood fibres from recycled newspapers), it is suitable for buildings where people with various allergies are often present. Werro Wool is especially suitable for insulating public buildings, such as kindergartens, schools, nursing homes, etc. It is sometimes thought that the boron compounds present in cellulose wool are hazardous for human beings. In fact this fear has no scientific backing. Boron compounds are used extensively in cosmetics and various products surrounding us in our daily life (including products made of fibreglass, reinforced plastic and LCD televisions). For customers’ confidence we are glad to declare that Werro Wool is manufactured according to a special recipe, in which most boron compounds have been replaced with other salts. Such recipe allows us to maintain and improve all the properties of the material (e.g., fire and vermin resistance), but also brings additional confidence for people who find boron compounds harmful for any reason whatsoever.

Environmentally friendly

Up to 85% of Werro Wool is made up of waste paper. Therefore it makes a significant contribution to recycling and the economic cycle. Werro Wool itself is recyclable – it can be collected from the structure of a house and reused as insulation.

Werro Wool is manufactured in Estonia from primarily local waste paper. Therefore the ecological footprint of the manufacturing process is smaller than that of several competing products. In the manufacturing process we use modern technology and cooperate with various international partners in order to obtain the most up-to-date information for developing our product. In manufacturing we meticulously follow quality standards as a result of which we have an ISO 9001 management system and ISO 14001, EMAS environment management certificates (you can examine public information here).

The kraft paper packaging of Werro Wool is also recyclable and we collect it in cooperation with our larger customers.

The Werro Wool factory is located in Võrumaa, Estonia – contributing to the development of businesses outside large centres. For us it is important to contribute to our community aside of our manufacturing activities. 


Werro Wool was granted the D-s2, d0 result (on the Euroclass scale) based on burning tests performed by TÜV Eesti OÜ, which means that the material has longer-term resistance to small flame (height 20 mm) and, in the case of a thermal impact, it is a material with slow and limited heat emission. This result was obtained by an independent laboratory and you can read the respective test protocol on our website under the Certificates and Tests section.

For fire resistance, salts are added during the fiberization stage, making up 15% of the product. We perform fire resistance tests for Werro Wool on a regular basis. For these purposes there is special equipment in our production facilities.

Many competing blown fibreglass wools belong to non-combustible category A. However, they melt as a result of heat, which in turn accelerates the spreading of fire in the constructions. The fire resistance of cellulose wool has been tested in many experiments. 

Vermin free

The boron compounds in Werro Wool keep rodents away from the insulating layer. The boron compounds also work well against mould and various fungi. This is especially important in case there is a water leak in the building. Werro Wool is a self-ventilating material that dries over time while preserving its insulating properties. At the same time, the boron compounds present in the material keep away mould and fungi.


Werro Wool has a great soundproofing ability, which is due to the flaky structure of the material. The result is a remarkable improvement in noise reduction of both external and internal walls.


Werro Wool is affordable due to following factors:

  • The installation of blown cellulose fibre is faster, more airtight and less expensive than with common roll or sheet wools.
  • When installing blown cellulose fibre, there is no need for vapour barriers (cost of material and time), as this already is included in the design stage.
  • The insulating quality of blown cellulose fibre is better than blown fiberglass and rockwools, which results in more long-term savings.
  • NB! If comparing quotations from different materials and installers, offers must be based on the densities of materials required by the manufacturer (see densities of Werro Wool on our website under the Installation section). Why is following the manufacturer-required densities important? Because at installation, a malignant mediator/installer may blow less material and more air into the bulk of wool layer, thus achieving a seemingly favourable cost. The result is an insulation that will drop off soon and has poor thermal resistance. As manufacturers, we cannot tolerate such practices as we care about the satisfaction of our customers.