Drying is the least glamorous step in PET processing and one of the most important. Skip it or get it wrong and the polymer degrades before it ever reaches the mould. Here is what drying does and why it protects your bottle.
Why PET must be dried
PET is hygroscopic — it absorbs moisture from the air. If wet PET is melted, the water triggers hydrolysis: the polymer chains break, intrinsic viscosity (IV) drops, and the resulting preform is weaker and more brittle. Drying removes that moisture before the melt.
The targets: dew point and time
PET is typically dried to a moisture level around 50 ppm or below, using a desiccant dryer delivering air at roughly −40 °C dew point, at ~150–175 °C, for about 4–6 hours of residence time. Too short and it stays wet; too long or too hot and you risk other issues. The exact window depends on resin grade and throughput.
Signs of wet resin
Under-dried PET shows up as bubbles or silver streaks in the preform, haze, an acrid smell, and lower top-load or burst strength from the IV loss. These are easy to misread as a mould or process fault — always rule out drying first (see common preform defects).
rPET needs extra care
Recycled PET often carries more moisture and a slightly lower starting IV, so drying discipline matters even more when blending rPET — see the rPET buyer guide.
Why it reaches your bottle
IV and AA on a preform spec are the visible output of good drying and melt control — they are what keep bottle strength and flavour consistent (see reading a preform spec sheet). Delta El Nile for Industry holds water, juice and dairy resin at IV 0.76–0.80 and tight AA. Build an RFQ with your application and we will confirm the grade.