Hot wash vs cold wash

The washing step defines a recycling plant's output quality. A cold wash uses ambient or warm water with friction to remove loose dirt and some labels — adequate for polyolefin films heading into dark products. A hot wash runs flake through water at 80–90 °C with caustic soda and detergent, dissolving glues, stripping label residues and saponifying oils.

For PET the distinction is decisive: only hot-washed flake achieves the glue and contamination levels that sheet extrusion, fibre spinning and — after super-clean decontamination — food-contact applications demand. Cold-washed PET trades at a marked discount into undemanding uses. The wash step also defines cost: heat, chemicals and wastewater treatment are why hot-wash lines are licensed, capital-heavy operations — and why "hot-washed" on a spec sheet is a claim worth verifying at the plant.