Animal, Vegetable or Mineral?
These fibres grow from plants or animals. If they are plant based they are built with cellulose, if they are animal based, they are built with protein, (corn based fibres break the rules here, protein from plant.) If they can be used after harvesting and washing (maybe a bit of long soaking and a lot of mechanical action too in the case of flax/ hemp/ some bamboo) then they are natural.
These usually consist of oil based constituents. These are entirely inventions of the industrial era, the main players here are Polyester and Nylon. Elastane, or Lycra ™ is Polyurethane and in this gang too! Essentially these are plastics that are extruded into fibres with a myriad of final properties and characteristics. Modern processing is now including post industrial and post consumer waste back into useable fibres, e.g. Polyester Fleece from plastic drink bottles, and Nylon swimwear fabrics from salvaged ghost fishing nets. Though this is a tiny fraction of the market.
Polyester is currently about 60% of the global annual fibre consumption.
Recycling – this can be possible with some synthetics, but the capacity to recycle fibres, globally, is very small, most end up in landfill and don’t biodegrade.