Mould susceptibility of supplemented mycelium composites for insulation applications

Abstract Mycelium-based composites (MBCs) are emerging as promising sustainable insulation materials because of their low embodied energy, low thermal conductivity and ability to utilise lignocellulosic waste. However, their organic composition and use of nutrient-rich supplements raise concerns regarding mould susceptibility, which may compromise durability, necessitate remediation or replacement and adversely affect indoor environmental quality and occupant health. This study investigated how supplementation influenced MBCs produced from beech sawdust, hemp shiv and wheat straw using Ganoderma curtisii . MBCs were produced without supplementation or with 10 and 20 wt% wheat bran or flour. Mycelial growth, density and thermal conductivity were assessed. Following 28 days at 90% RH and 25 ∘ C, mould susceptibility was evaluated using EN 17886:2023 ordinal ratings, image analysis of surface coverage, recovered spore density and mass change. Supplementation did not increase mould susceptibility. Mean mould coverage decreased from 25.2 ± 3.2% in unsupplemented composites to 10.2 ± 2.2% at 20 wt% supplementation, with similar trends in spore density, mass increase and ordinal ratings. Supplementation generally enhanced mycelial growth, while all formulations exhibited low thermal conductivity values of 0.033–0.055 W/m⋅K. Nevertheless, all formulations remained susceptible to mould growth under prolonged high-humidity exposure.