A growth area in wood-based panels is the softboard and insulation products market. While softboard has been a substantial niche product for many years – confusing many generations of students about the variations of uses (with names like pinboard, hobbyboard and insulation board), a growing interest in recycled and natural materials has changed the scene somewhat.
A larger effect is the emergence of woodfibre insulation – leading to further overlap of terms between insulation board and rigid batt insulation. These two products are often grouped together for statistical or market analysis purposes.
The whole family of softboard products is lightweight, meaning that it has quite good insulating properties compared to MDF or HDF. For example, softboard has a density around 380kg/m3, compared to the common MDF range of 500 to 800 kg/m3 or HDF density up to 1,450 kg/m3. This gives softboard a thermal conductivity of 0.07 W m-1K-1 compared to values in the range 0.11 to 0.22 W m-1K-1 for MDF. Lower values are better. Softboards with lower densities may reach conductivity values as low as 0.037 W m-1K-1. This value is within the range needed for building insulation products, and some insulation board is already used to reduce thermal effects in van fit outs, or to dampen sound either as an underlay for flooring or in acoustic applications. Low density boards typically give good sound insulation properties as well as their thermal benefits.
Many of the long-established softboards are classed as Natural Fibre Boards (NFB) a term that the EPF reserves for boards that contain no binding agents or synthetic resins. Typically, they are formed by the wet process, relying on hydrogen bonding between the fibres rather than adhesive.
There are also NFB hardboard products – which are again binderless systems, although higher density and for different applications.
However, recent statistics indicate growth in the softboard category – the EPF showed European production increased by 8% to 5.2 million m3 in 2024 (while PB and MDF increased by 1% each). Much of this relates to the rapid expansion of woodfibre insulation. Many woodfibre insulation products are dry process, so may use binders, unlike NFB softboard.
The growth of woodfibre insulation ties in with a drive for improving energy performance of new and existing buildings (retrofit can make excellent use of woodfibre insulation products), as well as customer desire to use natural, recyclable and low environmental impact materials. The breathable and moisture buffering benefits of natural insulation products are in great demand to enhance indoor air quality and a healthy built environment.
This brings us to the technical component of this month’s article – looking at thermal performance.
The thermal conductivity shown above for low density softboard (0.037 Wm-1K-1) is very similar to that reported for the thicker rigid woodfibre insulation products (eg 0.038 to 0.041 W m-1K-1). So how do we measure performance of thermal insulation properties?
Thermal conductivity (λ) can be measured using a hot box method, with two different temperatures applied on the opposing faces of the panel.
The difference between these two temperatures (ΔT) is controlled to run the experiment. The time for temperature stabilisation is measured and indicates the heat flow rate (Q) across the thickness of the panel. The area of the panel surface (S) and the thickness of the panel (t) are taken into account, as a larger area will increase the quantity of heat that can move, while thicker panels will decrease this.
The resulting thermal conductivity value is given in Watts per metre per Kelvin (W m-1K-1). Of course, one Kelvin is the same size as one degree Celsius (even if the zero temperature is different, 0°C is 273.15K). To input the temperature difference, we can simply subtract our cold plate temperature, eg 10°C from the hot plate temperature, eg 35°C, giving ΔT of 25K.
The thermal conductivity value can then be used with product thickness information and the wall design details to calculate the U-values of the building made using with the insulation product.
