A natural fiber is collected from plants or animals. It’s that simple.
Some textile fibers are semi-synthetic. Semi-synthetic fibers are derived from a naturally occurring fiber through a chemical process. So basically, the naturally occurring fiber is harvested, broken down, and then reconstructed. This is most commonly done with cellulose. Cellulose is a structural component abundant in plants. The cellulose is extracted from the plant, made soluble, and then spun into fiber. In many cases, this process can be done sustainably and yields a very versatile fabric. Examples of fabrics made from cellulose include: rayon, viscose, modal, lyocell, and Cupro.
Essentially, most synthetic fiber is plastic. Synthetic fiber is manmade through the process of polymerization. Manufacturing begins with chemicals like sodium hydroxide and carbon disulfide. These chemicals are derived from natural gas, coal, and oil. The chemical solution is pushed through spinnerets (tiny holes) into air or water. As the chemicals come out of the spinnerets and cool, they solidify and form threads. These threads are then bonded together into a textile. Additional chemical processes will be used to treat the textile depending on the desired qualities of the final product (water resistant, stain proof, wrinkle free, antistatic, etc.).
Unfortunately, the production of synthetic fibers has a high impact on the environment. A great deal of energy, water, and natural resources (that are non-renewable) are used. There are also a number of harmful byproducts created. Further, clothing made with synthetic fiber sheds microscopic pieces of plastic throughout their product life. After synthetic clothing is discarded, it can stay in the landfill for hundreds of years, while leeching toxins.
Synthetic fabrics are more likely to harbor bacteria and absorb environmental toxins. Studies have also revealed that even plastics that are tested to be BPA-free emit endocrine disruptors (similar to BPA) when exposed to normal everyday wear.