Paul Wheaton. 2021. Podcast 518 - Insulation made from Mushrooms, from the permies.com Permaculture Podcast. Available from https://permies.com/wiki/150646/Podcast-Insulation-Mushrooms.
From the episode's description:
Wood and straw bales have an r-value of 1-2/inch – not that much, but quite a bit when a bale is 18” thick. Mycelium boards r-value depends on its density and how completely it consumes its substrate, but is usually comparable to rockwool which has an r-value of between seven and twelve, and up to 17 per inch. Rockwool has an r-value of 5/inch.
In order to keep the mycelium from trying to turn your house into a compost pile, it has to be baked. This presents a problem because you have to bake the inside of a thermal insulator. More problems come from trying to cut the stuff, with the best fungus for insulation so far also being very difficult to cut from a combination of simple toughness, its fibrous nature, and its tendency to gum up sawblades. Water jet cutting is out of the question, seeing as adding water to the insulation might make more mushrooms rather happy.
The substrate will need to be inoculated with spores, then kept warm and moist for about 10 weeks before being ready to cook. When done, it’s non-flammable, mice don’t like it, repels insects, and resists mould. Plus, the substrate produces mushrooms while it’s growing, which is just added value, although getting more than one crop will mean having to delay getting the insulation.
When ready to cook, the mycelium can be removed from their trays as they’re rigid, and cooking the insulation requires the temperature to reach 200F for about four hours to stop it from growing. Killing the spores requires the temperature to be higher, but they need water to grow, so unless there’s water seeping into your house, there’s not much chance of mushrooms sprouting from your walls, and if there is, there’s bigger problems.
See also the Mushroom Insulation thread in the 'Natural Building' forum at permies.com.
Also to review:
See, for example, Is Mycelium Fungus the Plastic of the Future?