Gramitherm, a Belgian biobased insulation

Production

Auvelais, province of Namur

Capacity

180,000 m³ a year · 3,000 houses

A grass-fibre panel seen in section, resting on a grid, against the light

For 15 years, Gramitherm has been developing an insulation material made from grass residues. Since 2022 the company has been based in Belgium, in Auvelais, where it produces its boards and rolls for construction.

Grass as a raw material

The grass used comes from areas excluded from the food chain: road verges, airports, wetlands. The association that maintains these areas cuts around 1.5 million tonnes of grass a year.

Just 2.2% of this quantity is enough to run the production line at full capacity, with an output of 180,000 m³ of insulation a year, the equivalent of 3,000 insulated houses.

Manufacturing process

Once the grass has been collected, the juice and the fibre are separated. The juice is turned into biogas, which is used to dry the fibre.

Grass fibre makes up 72% of the raw material of the finished board. It is mixed with 20% jute fibre and 8% synthetic fibre, the latter being needed to bind the fibres together.

The mix is compressed and then spends two minutes in an oven at 160 °C, a short bake that uses considerably less energy than the manufacture of a conventional insulation material.

Bales of compressed grass stored before processing, close-up of the fibre — Compressed grass, before processing.

Grass-fibre boards stacked at the end of the line, an operator in a hi-vis vest in the foreground — The boards, at the end of the line.

Stack of grass-fibre boards seen at an angle, with thicknesses and densities visible on the edge — Thicknesses and densities, on the edge.

The data

Negative carbon footprint, λ of 0.040, high thermal phase shift.

Embodied carbon

By the end of its manufacture, one kilogram of Gramitherm insulation has stored the equivalent of 2.08 kg of CO₂ and generated only 0.675 kg of CO₂ emissions.

The result: a negative carbon footprint of -1.4 kgCO₂/kg, against +7.36 kgCO₂/kg for an EPS board of equivalent performance.

Thermal performance

Thermal conductivity λ: 0.040 W/mK · to reach an R-value of 4, a thickness of 16 cm is enough, barely more than with stone wool
Thermal phase shift: high, as is typical of biobased insulation · protects against summer overheating
Vapour permeability: good, contributes to the vapour openness of the wall

Installation and economics

Gramitherm is installed in the same way as a flexible wool-type insulation, without the itching for installers.

Because the product is made locally, its price is more stable than that of products exposed to international trade. On the Belgian market in 2024, Gramitherm was priced below stone wool.

A biobased insulation gives access to regional grant top-ups: €10/m² in Brussels and a 25% top-up in Wallonia (subject to the “Produit biosourcé” label).

The material
in this article

Gramitherm · grass-fibre insulation Gramitherm · the producer, in Auvelais