Flax insulation - a natural and ecological insulation


Flax fiber is a natural and ecological insulating material that comes from native resources and optionally manages without synthetic additives. Flax insulations are vapor-permeable, have good thermal insulation properties and offer good sound and heat protection.

Flax insulations are obtained by mechanical treatment from the stems of the flax plant. Just like hemp fibers, they are produced by the so-called random fiber process: the flax fibers are roasted, broken, beaten, combed (hackled) and then processed into a fiber fleece. Corn or potato starch is used as the adhesive, in some cases other vegetable fibers (jute) or polyester fibers are used as support material. As flame retardant, the fiber-starch mixture is impregnated with boron salts.

Table 1: An overview of the properties of coconut fibers

thermal conductivity0.04 W / mK
Building material classOld: B2, New: E (normally flammable after adding boron salts)
minimum insulation thickness according to EnEV 201415 cm
density20 - 80 kg / m3
Price per m213 - 30 EUR

How do flax insulations come into the trade?

Flax insulation is offered in the form of boards, fleeces, mats and as stuffing wool. In addition, there are also composite building materials on flax fibers, for example as a combination of flax and loam. On the insulation market, flax fibers are playing a secondary role, partly due to their limited use. They are produced by various manufacturers of natural building materials. With a m2 price between 13 and 30 euros, they can easily compete with conventional insulating materials such as mineral wool or polystyrene-based plastic insulation (EPS, XPS).

What are the building physics properties of flax insulation?

The thermal conductivity (lambda) of flax fibers is 0.04 W / mK (watts per meter x Kelvin).
With this value, the insulation performance of a flax insulation in the lower part of the thermal insulation effect of mineral wool or polystyrene moves. Due to its water vapor diffusion resistance of 1 to 2? Flax fibers are a strongly diffusion-open and capillary-active insulation material and thus ideally suited for old building or monument renovations, where it depends on an optimal moisture regulation by the insulating material. Due to their fiber structure, flake insulation has good to very good heat and sound insulation properties.

Table 2: Hemp and other thermal insulation products in comparison

insulation materialsThermal conductivity (W / mK)Minimum insulation thickness according to EnEV (cm)Cost per m2 (Euro)
flax0,041513 - 30 EUR
hemp0,04 – 0,0451610 - 27 EUR
coir0,04 – 0,051835 - 55 EUR
rock wool0,035 – 0,0401410 - 20 EUR
EPS / Styrofoam0,035 – 0,045145 - 20 EUR

Fields of application of flax insulations

Since flax insulations are mechanically only very limited and are also resistant to moisture only for a short time resistant to moisture, come for this insulation only limited applications in question. For external insulation of facades or roofs, they are not suitable. Flax insulations are used for example for:

  • Interior insulation of exterior walls: Due to their diffusion-openness and capillary activity, flax insulation is ideally suited for the internal insulation of exterior walls.
  • Insulation of walls in wooden frame or wood panel construction
  • Roof insulation of roofs
  • Thermal and acoustic insulation of partitions indoors
  • ceiling insulation
  • Cavity Insulation: Clogged wool made of flax fibers can be used for cavity insulation in roof, column and beam constructions.

Advantages of flax insulations:

  • Good thermal insulation properties
  • Very good heat and soundproofing capabilities
  • Open to diffusion and capillary activity
  • Easy processing with wood tools
  • Pollutant-free, recyclable.

Disadvantages of flax insulations:

  • flammability
  • Limited application options: Flax insulations can only be loaded mechanically to a limited extent. They are only resistant to moisture and weather conditions for a limited period of time.

Tips & Tricks

Flax fiber is a natural insulating material derived from renewable, indigenous resources. They have good thermal insulation properties, ensure good moisture regulation of the building and provide effective sound and heat protection. Due to their limited resistance to mechanical stress, the effects of the weather and moisture, flax insulation can only be used in internal, dry building areas.


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