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Hot-Washed vs Cold-Washed rPET Flakes: What's the Difference?

Hot-washed rPET flakes are washed in heated caustic water (~60–80°C), stripping glue, oils and residues for a cleaner, higher-value flake. Cold-washed flakes use ambient water, cost less, but only remove surface dirt.

Materials Guide · 22 Jul 2026 · 6 min read
Hot-Washed vs Cold-Washed rPET Flakes: What's the Difference?

Key takeaways

  • Temperature is the core difference: hot wash uses heated caustic solution; cold wash uses ambient water.
  • Hot washing removes glue, grease and adhesives that cold washing leaves behind.
  • Hot-washed flake commands a higher price and suits demanding applications; cold-washed is cheaper for tolerant ones.
  • Neither is automatically food-grade — food contact needs a separately approved decontamination process.

What is the difference between hot-washed and cold-washed PET flakes?

The difference comes down to wash temperature and chemistry. Cold-wash lines run at roughly 10–20°C and mainly rinse off surface dust and loose contamination. Hot-wash lines heat the water to around 60–80°C and add an alkaline (caustic soda) solution, which dissolves label glue, grease and oily residues — producing a noticeably cleaner, higher-purity flake. As a rule, hot-washed flake is better quality and priced higher; cold-washed flake is cheaper and uses less energy.

Hot-washed vs cold-washed: side by side

Hot-washedCold-washed
Wash temperature~60–80°C, caustic solution~10–20°C, ambient water
RemovesGlue, oils, grease + surface dirtSurface dirt only
Grade & priceHigher grade, higher priceLower grade, cheaper
Best forFibre, sheet, packagingStrapping, lower-spec uses

Which grade should you buy?

Match the grade to the tolerance of your process:

  • Polyester staple fibre & filament, PET sheet, thermoforming, packaging — choose hot-washed flake for cleaner melt behaviour and fewer defects.
  • PET strapping and less demanding moulding — cold-washed flake often delivers the strength you need at a lower cost.
  • Appearance-critical clear sheet — hot-washed, colour-sorted flake with low black-speck and contamination counts.

Whatever the grade, the numbers that matter to your line — intrinsic viscosity, moisture and contamination — should come on a Technical Data Sheet and a per-lot Certificate of Analysis. See our guide on how to read an rPET COA.

Does hot washing make rPET food-grade?

No. Hot caustic washing improves cleanliness, but food-contact recycled PET additionally requires an officially assessed decontamination process — an FDA "No Objection" letter in the US or an EFSA positive opinion in the EU. We cover this in Is recycled PET food-grade?

Frequently asked questions

Is hot-washed or cold-washed PET flake better?
Hot-washed flake is cleaner and more consistent because heated caustic water removes glue, oils and residues, so it suits higher-grade fibre, sheet and packaging. Cold-washed flake is cheaper and lower-energy and works for strapping and less demanding uses.
What temperature is used for hot washing PET flakes?
Hot-wash lines typically run around 60–80°C with added caustic soda; cold-wash lines run near ambient temperature (about 10–20°C).
Does hot washing make rPET food-grade?
No. Hot washing improves cleanliness but does not, by itself, make recycled PET food-contact approved. That requires an officially assessed decontamination process (FDA no-objection letter or EFSA opinion).

Sources: Recycling Machines — Hot vs Cold Washing; Energycle — Cold vs Hot PET Washing Lines.

Let's Talk Recycling

Need hot- or cold-washed rPET flakes?

Tell us your application and volumes and we'll recommend the right grade — with a matched Technical Data Sheet.

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