PET for water, carbonated drinks and hot-fill: what is the difference
Three bottle grades, three different sets of requirements for viscosity, strength and heat resistance. We explain why one grade cannot simply be swapped for another.
All three are food-grade bottle PET, and the pellets look almost identical. But a bottle for water, a carbonated drink or a hot-filled product works under different conditions, so the resin requirements differ too.
The key parameter: intrinsic viscosity
Intrinsic viscosity (IV) reflects the length of the polymer chains. The higher it is, the stronger and more load-resistant the bottle wall, but the more effort and energy processing takes. That is why each product gets its own range: strong enough, but without unnecessary margin.
Three products, three sets of requirements
Water
Still water creates no pressure in the bottle, so a moderate viscosity is enough for the water grade. The priorities are:
- bottle clarity and gloss;
- neutral taste — for this, the industry monitors acetaldehyde content;
- stable processing of lightweight preforms on high-speed lines.
Carbonated drinks
A bottle of a carbonated drink stays under pressure for the whole storage period. The CSD grade needs a higher viscosity so that:
- the bottle does not deform or expand, especially in warm conditions;
- the petaloid base does not stress-crack;
- the wall retains carbon dioxide and the drink keeps its carbonation until the end of its shelf life.
Hot-fill
Juices, tea and isotonic drinks are often filled hot. A standard bottle shrinks when heated, so hot-fill bottles are blown with heat-setting in a heated mould. The hot-fill grade must crystallise predictably and give a strong wall, while the bottle design compensates for the vacuum that forms as the product cools.
Can one grade replace another?
Sometimes, but not without consequences. A water grade in a CSD bottle risks failing under pressure. A grade with excess viscosity on a water line will need different settings and will raise energy costs. In hot-fill, the blowing technology matters as much as the grade, so switching without trials is not recommended. If you are moving to a different grade or launching a new product, start with a trial run on a small lot.
Not sure which grade you need? Describe your product and equipment — we will select a grade and send the TDS and a sample for a trial run.