Intrinsic viscosity — IV — is the number buyers and engineers quote most about PET resin, and the one most often misunderstood. In plain terms, here is what it is and why it decides how your bottle performs.
What IV actually measures
IV (in dl/g) is a stand-in for the average length of the PET polymer chains — its molecular weight. Longer chains mean a higher IV, which means more strength and melt toughness. It is measured by how much the resin thickens a solvent — hence “viscosity.”
The IV scale by application
Different products need different IV:
- Water, juice, dairy: ~0.76–0.80 dl/g — lighter walls, lower stretch demand.
- CSD, edible oil, detergent: ~0.84 dl/g — must hold pressure or resist aggressive contents.
- 5-gallon / 19 L returnable: ~0.84–0.87 dl/g — heavy, reused, maximum toughness.
Higher is not automatically better — too high an IV is harder to process and wastes cost where it is not needed.
Why IV drives the bottle
IV sets how far the preform can stretch without weakening, the bottle’s top-load and burst strength, and how cleanly it blows. Pick the right IV for the application and the bottle is strong and economical; pick wrong and you over- or under-build it.
How IV drops — and why it matters
IV falls when PET is processed wet (hydrolysis) or over-heated (thermal degradation). That is why drying and melt control matter — they preserve the IV you paid for. A spec sheet lists IV precisely so you can verify it (see reading a preform spec sheet).
What Delta holds
Delta El Nile for Industry matches resin IV to the application — 0.76–0.80 for water/juice/dairy, 0.84+ for CSD/oil and 5-gallon — verified per lot. Build an RFQ and we will confirm the grade for your bottle.