Plastic materials of natural origin in expanded form for industry, in particular for the manufacturing of furnishings, mattresses, pillows and cushions, clothing, packaging, and for use in the automotive industry, and personal hygiene industry; flexible expanded polyurethane of natural origin, in particular for the manufacturing of furnishings, mattresses, pillows and cushions, clothing, packaging, and for use in the automotive industry, personal hygiene industry, and medical devices industry