The goal of this study is to design an organic material that will be 100% compostable at the end of its useful life. The material is composed of the mycelium of Pleurotus ostreatus grown rye grains and white ash chips. The white ash chips were locally sourced from the activities in the City of Montreal. The objectives are to develop a protocol for the culture of the material and to characterize it and compare it to glass wool and hemp wool, which are two proven insulators. The mycelium is the binder and two sizes of white ash chip were tested: thin and medium. The thermal conductivity was measured using the modified transient plane source sensor. The mycelium on the medium size chip produced the best-isolating properties better than the glass wool and hemp wool. The R factor in SI unit was 15. The wood chip also provided strength to the material. Grown at ambient temperature, its low carbon footprint and its absence of synthetic products make mycelium material an environmentally responsible material choice.