A fungus, Mycelium, is being talked about as an alternative to plastic to make things
Basically, they make a mold and then fill it with hemp or woodchips (or some other agricultural waste). This is called the 'foam.' Mycelium is also placed in the molds. The molds are then placed on racks with temperature, humidity, co2 and airflow controlled.
The Mycelium fibers grow so they fill the mold. Then the molds are heat treated to kill the Mycelium.
Some people are also making other products such as bacon and other artificial meats, a leather alternative, insulation, and fabrics out of Mycelium.