Cellulose - powerful, cheap, environmentally friendly


Cellulose is an organic insulating material consisting mainly of recycled waste paper. It impresses with its excellent thermal insulation performance and good heat and sound insulation properties. Cellulose is in first place in the market segment of ecological insulation materials.

In Scandinavia and North America, cellulose was used more than 100 years ago for thermal insulation. In the course of growing interest in ecological construction, it has been playing a steadily growing role in the insulation market for several years. Cellulose insulation is quite versatile. Compared to other ecological insulating materials, cellulose also offers very economical thermal insulation due to its low price. Due to its low bulk density, cellulose is very well suited for lightweight construction. Disadvantages lie mainly in the low moisture resistance of the material: with the exception of buildings in timber frame construction, cellulose is therefore not approved for facade insulation. Cellulose holds a market share of about 30% in the market segment of ecological insulating materials, thus taking first place. However, the total market share of ecological insulation materials in Germany is below 10%.

Table 1: Overview of the properties of cellulose

property
thermal conductivity0.04 - 0.045 W / mK
Building material classAlt: B2 (normally flammable)
minimum insulation thickness according to EnEV 201416 cm
Bulk density cellulose flakes30 - 80 kg / m3
Bulk density cellulose plates80 kg / m3
Price per m210 - 20 EUR

Which starting materials are contained in cellulose insulations?

Cellulose (cellulose) is the main component of plant cell walls. From the perspective of chemists, it is considered the most common organic compound and the most common polysaccharide (polysaccharide). In plants, the cellulose molecules often form tear-resistant fibers that assume static functions. Cellulose in its original or recycled form is the most important raw material for papermaking. Cellulose for thermal insulation consists of 80 to 90% recycled paper. As flame and rot protection, 12 to 20% borax, boron salts or ammonium polyphosphate and 2% natural resins are added to the fiber mixture.

How is cellulose produced for thermal insulation?

The production of cellulose flakes for thermal insulation takes place in a few steps: The recycled paper is shredded, blended with additives and converted into fibrous flakes in a multi-stage tearing and grinding process. Cellulose insulation boards are pressed under the action of water vapor. The steam activates the natural binders present in the cellulose, to stabilize the plates often other natural fibers - such as jute material - used.

How do cellulose insulations get into the market?

In the vast majority of cases, cellulose is used for thermal insulation in flake form. In addition, there are cellulose insulation boards or mats, which are usually offered in thicknesses between 30 and 180 mm.

Cellulose - a favorable ecological thermal insulation material

With a price of 10 to 20 EUR per m2, cellulose is one of the most affordable insulation materials on the market. By comparison, wood-fiber insulation panels, which are also considered ecological insulation, cost between 40 and 50 euros per m2. For cork between 20 and 30 EUR, for coconut fiber between 35 and 55 Euro and for Perlite between 20 and 45 EUR. In contrast, the price of cellulose flakes and cellulose plates is at the same level as for common insulating materials such as mineral wool (glass and rock wool) and the EPS / Styrofoam or XPS plastics.

Manufacturer of cellulose for thermal insulation

Many manufacturers of cellulose for thermal insulation are also active in the market with other recycled products. Well-known manufacturer and brand names are, for example, isofloc, CWA / climacell or Homann (Homatherm) insulation plants.

What are the building physics properties of cellulose?

The thermal conductivity of cellulose is between 0.04 and 0.045 W / mK (watts per meter x Kelvin) regardless of its use as cellulose flakes or plates. In terms of their insulation performance, they are about the same as plastics such as EPS or XPS. Mineral wool is sometimes slightly superior to cellulose in terms of thermal insulation capabilities. The insulating effect of cellulose results from the inclusion of air in the inter-fiber spaces.

Good heat and soundproofing capabilities

Due to the dormant trapped air between the fibers, cellulose also has good heat and sound insulation capabilities. These ensure that heat and sound waves penetrate into the building significantly ahead of time.

Open to diffusion and capillary activity

Cellulose is a highly permeable and capillary-active insulating material. The water vapor diffusion resistance of a thermal insulation with cellulose flakes is only 1 to 2?. Cellulose insulation is thus ideally suited for renovation of old buildings and / or the interior insulation of exterior walls, which places particularly high demands on the capillary activity of the insulation for a sustainable moisture balance. For comparison: Because of their diffusion-openness and capillary activity, calcium silicate boards are the preferred material for the thermal insulation of old houses, their water vapor diffusion resistance is between 5 and 20 ?.

Limited fire protection properties

Cellulose is a combustible material. Its flashpoint is 164° C. The addition of flame retardants optimizes their fire protection properties.

Table 2: EPS and other thermal insulation materials in comparison

insulation materialsThermal conductivity (W / mK)Minimum insulation thickness according to EnEV (cm)Cost per m2 (Euro)
cellulose0,04 – 0,0451610 - 20 EUR
glass wool0,032 – 0,0401410 - 20 EUR
EPS / Styrofoam0,035 – 0,045145 - 20 EUR
Wood fiber insulation boards0,04 – 0,551840 - 50 EUR
Calcium silicate boards0,0652080 EUR

DIN standards, building material classes, EnEV

The EU standard DIN EN-13501-1 assigns cellulose to building material class E (normally flammable); the addition of flame retardants makes it possible in some cases to classify it as B - s2 d0 (partially flame retardant). According to the old national DIN standard 4102-1 it belongs to building material class B2 (normally inflammable). Cellulose insulations without flame retardants play no role in practice. In order to meet the requirements of the Energy Saving Ordinance (EnEV) 2014, a cellulose insulation must have a minimum insulation thickness of 16 cm.

Cellulose insulation is made from recycled paper. They consist of 80 to 90% cellulose fibers. Their use is mainly in the form of cellulose flakes, in addition, thermal insulation is carried out with cellulose plates or sheets.

Fields of application of cellulose insulation

Cellulose insulation can be used relatively flexibly in dry building areas. Cellulose is mainly used for:

  • Roof insulation: For roof insulation cellulose is used in the form of sheets or sheets as well as spray insulation.
  • Inter-parquet insulations, insulation of the sloping roofs and the attic: For these types of insulation cellulose is usually used as (more or less strongly compressed) blow-in insulation.
  • Ceiling and floor insulation: Cellulose fibers are also used as loose bulk insulation for the thermal insulation of floors or ceilings - including subsequent insulation of the top floor ceiling. Among other things, cellulose causes excellent impact sound insulation.
  • Facade insulation: A facade insulation with cellulose is only suitable for buildings in timber frame construction.
  • Interior insulation of exterior walls: A classic field of application of cellulose insulation is the interior insulation of exterior walls in old building renovation as well as in the thermal insulation of listed buildings. Due to their diffusion properties and their capillary activity, cellulose is particularly well suited for this type of insulation. In double-shell constructions blowing insulations are also possible here, otherwise the thermal insulation takes place by means of insulation boards or applying the cellulose flakes in a spray-on process.
  • Thermal insulation in interiors.
  • Thermal insulation composite systems (ETICS): In the context of ETICS, cellulose insulation is mainly used in combination with other ecological thermal insulation materials, such as wood fiber insulation boards.

Advantages of thermal insulation with cellulose

Advantages of thermal insulation with cellulose are:

  • Excellent thermal insulation capabilities.
  • Economy due to low prices and moderate insulation thickness.
  • Dimensional stability: Even cellulose flock insulation has high dimensional stability. Unlike granule insulation materials such as perlite, the cellulose flakes can be pressed and compacted to a great extent even with blow-in insulation. Flake insulation with cellulose flakes optimizes this property.
  • Elasticity: Thermal insulation panels, mats or sheets of cellulose are highly elastic and thus adapt to the most diverse structural conditions.
  • Diffusion-openness and capillary activity: Cellulose is highly permeable and capillary-active. Due to their very low water vapor diffusion resistance, cellulose insulation is therefore also excellently suited for the interior insulation of exterior walls.
  • Good heat and sound insulation properties: Depending on the manufacturer and the consistency of the insulation, the soundproofing effects of cellulose can be up to 49 dB.
  • Low weight: Due to their comparatively low bulk density, cellulosic insulations are also suitable for thermal insulation of pitched roofs and other weight-sensitive areas of buildings.
  • Outstanding Life Cycle Assessment: Cellulose is a natural and renewable resource. The energy balance in their industrial production is also favorable.
  • Pest and mold protection: Cellulose insulations are protected by additives against pest infestation and are largely mold-resistant.

Disadvantages of a cellulose insulation

Disadvantages of a cellulose insulation are

  • Low mechanical load-bearing capacity of the insulating material: Cellulose insulation can only be used where there are few or no requirements for the mechanical strength of the insulating material. Although cellulose floor or ceiling insulation is effective in terms of insulation performance and sound insulation, mechanical loads must be cushioned by other materials.
  • Limited moisture resistance: Cellulose insulations can essentially only be used in a dry environment. The material is not moisture resistant and - once soaked - difficult to re-dry.
  • Flammability: Most cellulosic insulations are normally flammable even after the addition of flame retardants and burn even at comparatively low temperatures. In individual cases, the fire protection properties of cellulose insulation can be optimized to the status "partially flame retardant". In case of fire, no explicitly toxic emissions are released.

How is cellulose processed?

When working with cellulose, it depends on the consistency in which the material is to be used:

  • Blow-in insulation: Blow-in insulation is a typical field of application for cellulose. They may only be made with special equipment.
  • Bulk entrainment: bulk material with cellulose does not have any special technical requirements. From a building law perspective, they can also be made as own contribution.
  • Spray insulation: Cellulose spray insulation is a new process. For this purpose, the cellulose flakes are moistened, mixed with small amounts of adhesive and sprayed onto the wall with the aid of special equipment. This method creates a plate-like insulating layer up to 120 mm thick, which adapts to the walls exactly and seamlessly, even in the case of unevenness or difficult designs. Again, the expertise of a specialist is needed. Spray cellulose is mainly used for interior insulation in historic buildings, a flat wall surface is then created, for example by the application of clay or lime plaster.
  • Cellulose plates: Thermal insulation boards as well as mats or sheets of cellulose are glued. The processing can be done with the usual wood tools.

Dismantling, recycling, disposal

The dismantling effort for a cellulose insulation is low. On or inflated loose cellulose flakes are recyclable and can at least theoretically be used again as insulating material. Cellulose is landfillable without any special conditions. Cellulose is disposed of properly within the scope of normal waste incineration.

Health safety and health and safety

Used cellulose is a completely harmless health-promoting insulating material, it does not release any harmful emissions. Some products have independent certificates of their pollution-free status. Cellulose insulation with a waste paper content of at least 80% comes with the Ecolabel RAL-ZU 36 in the trade.

Fine dust emissions during the installation phase

In the installation and processing phase of cellulose insulation, particulate matter pollution was measured, which exceeds the so-called TRK value - the technical standard concentration - by a multiple of 2 mg / m3. In the case of blow-in insulation with cellulose, 11 mg of fine dust are released per m3, while the use of sprayed cellulose produces 21 mg / m3 of fine dust. Although there are no official limit values ​​for the detrimental effects of cellulosic dusts on the part of the construction industry, a potential carcinogenic effect is suspected, similar to the RTK value for wood dust. Above all, the regular, professional handling of cellulose insulations is therefore the maintenance of appropriate health and safety regulations (mouth protection, breathing mask) indispensable. With blown insulation with cellulose flakes, the dust load can be significantly reduced by a closed injection and suction circuit.

Tips & Tricks

Cellulose insulation can be used in many ways, but can only be done in dry areas of the building. Due to its diffusion properties and its capillary activity, this insulating material is ideal for renovation of old buildings and for interior insulation of exterior walls.


Video Board: Insulating Walls with Dense Packed Cellulose