Polyester is made through a chemical reaction involving coal, petroleum (from crude oil), air and water. The making and disposing of polyester have a massive environmental cost. As an oil-based plastic, polyester does not biodegrade like natural fibres. Rather it stays in landfills for several decades at least – and potentially for hundreds of years.
Recycled polyester is not a sustainable alternative for us. Multiple studies have shown that synthetic fibres make up a good share of microplastics found in waters and are widely implicated as the source of pollution. The main challenge of recycled polyester clothing is that it is not guaranteed to be recyclable. Plastics bottles tend to be mechanically rather than chemically recycled, which means they’re chopped up into flakes, melted down, and then extruded through spinnerets to create yarn for knitting or weaving into textiles.
Recycled PET manufactured this way cannot be mechanically recycled a second time, let alone multiple times, without a steep decline in the quality of the fibres, which get progressively shorter and weaker.