Wood fibre insulation: what it is and what problems it solves
Boards and flexible insulation made from wood. They go on walls outside and inside, on roofs and on floors. They keep out the cold in winter and the heat in summer and do not trap moisture in the construction.
What it is
Softwood is broken down into fibres. Two kinds of insulation are made from them: a flexible one that looks like mineral wool, and rigid boards that look like dense cardboard. The rigid boards are pressed under pressure at high temperature, and paraffin makes them water-repellent. naturheld insulation is made in Germany.
Light and flexible. It goes between roof rafters, between the studs of a timber wall, between floor joists and in partition walls. It is cut slightly wider than the gap and holds itself in place.
→Rigid boardsnaturheld 110 · 140 · 180 · 220Dense and strong — they can be rendered, walked on and glued. They go above the rafters, on the facade under render, on the inside of walls and on floors. The number is the density: the higher it is, the stronger the board.
→Where it goes
FLEX between the studs, a naturheld board outside as the wind barrier.
Wall from the insideWhen the facade cannot be touched — a board glued over the whole wall and lime plaster.
RoofNew — between and above the rafters. Old — from above, without opening the rooms.
FloorOn a concrete slab or between the joists of a ventilated floor.
All the layers, the tapes and the prices per m² — in “The system” →
What problems it solves
Wood fibre stores about twice as much heat per kilogram as mineral wool and is much denser. The heat from the roof reaches the room hours later — in the evening, when you are already airing it.
Insulation raises the surface temperature of the wall on the room side. In an example from the German wood fibre handbook, a solid brick wall insulated from the inside with 80 mm goes from 13.4 °C to 19.5 °C at 22 °C in the room.
The material lets vapour through — moisture gets out instead of being locked in behind the insulation.
A flat, a stone facade, a party wall — you insulate from the inside with the same material, room by room.
The roof is insulated from above: a membrane and a naturheld board on the old roof, then the tiles go back.
The dense fibres absorb sound. In an example from the handbook, an old roof renovated with wood fibre reaches up to 59 dB sound insulation according to a test report.
Honestly: when it is not the best choice
- If you want the lowest price per square metre — mineral wool and EPS are cheaper.
- If the design requires a non-combustible material (class A1) — then it is stone wool. naturheld boards are class E to EN 13501-1 (B2 to DIN 4102-1).
- If the construction stays wet or the roof leaks — stop the water first. No insulation tolerates prolonged wetting.
How it is installed
No special machines. The flexible insulation is cut with a saw slightly wider than the gap and pressed between the rafters. The boards are glued or fixed depending on where they go and are rendered or covered. On the inside, the airtight layer — a vapour control membrane or ESB — is sealed with tape. Details in the manufacturer’s instructions:
- Roof installation — naturheld instructions (PDF, in Bulgarian)
- Wall and facade — naturheld processing guidelines (PDF, in Bulgarian)
- naturheld FLEX — processing instructions (PDF, in Bulgarian)
Questions
Does it burn?
Wood fibre is a combustible material: naturheld boards are class E to EN 13501-1 (B2 to DIN 4102-1), while stone wool is non-combustible (A1). In a fire wood fibre does not melt or drip but chars slowly. In a finished wall or roof the fire resistance depends on the whole build-up — render, plasterboard, cladding.
Does it go mouldy or rot?
Not in a correct construction. naturheld boards contain paraffin as a water repellent and tolerate temporary moisture. The material lets vapour through and does not trap it in the construction. Like any insulation, it must be protected from prolonged wetting and leaks.
How much more expensive is it than mineral wool?
Per square metre, mineral wool and EPS are cheaper. Wood fibre is worth it when you need summer heat protection (attic room, loft), when the wall must stay vapour-open (old house, timber house) or when one board does the job of two layers.
Can my builder install it?
Yes. The flexible insulation is cut and fitted like mineral wool, and the boards like EPS. We provide the manufacturer’s instructions and help by phone. If you have no installer, write to us and we will help.
Is inside or outside better?
Outside is the better solution when possible: lower risk of condensation and no thermal bridges. You insulate from the inside when the facade cannot be touched. Wood fibre insulation is one of the few materials used in both cases.
More on naturheld.bg (in Bulgarian): What wood fibre insulation is · Insulating from the inside
Tell us what you are insulating
Roof, wall or floor, the area and the town — we reply with a proposal for the layers and a quote within one working day.
No installer? Write to us and we will help.