PET IV Matters: How Intrinsic Viscosity Affects Performance and Trade Decisions

What is the Intrinsic Viscosity (IV) of PET?

Polyethylene terephthalate (PET) is a widely used polymer material, commonly applied in beverage bottles, fibers, films, and engineering plastics. PET is valued for its transparency, lightweight, chemical resistance, and recyclability, making it a preferred material in modern packaging and industrial applications.

The intrinsic viscosity (IV) is a key indicator of the molecular weight of PET. A higher IV value indicates longer polymer chains, resulting in a  "heavier"  material with superior mechanical properties. Conversely, PET with a lower IV has shorter chains, better flowability, and is easier to process.

IV directly affects PET's processing performance, including melt flow behavior, stretchability, and suitability for blow molding. In simple terms, high-IV PET behaves like thick honey—dense and robust but less fluid, while low-IV PET is like thin honey—more fluid and easier to mold into complex shapes.

IV 0.78 as a Threshold in International PET Trade

In international trade, the intrinsic viscosity (IV) of PET is commonly used as a classification standard, with IV 0.78 serving as the typical threshold (some markets or suppliers may reference 0.72). Generally, low-IV PET refers to products with IV ≤ 0.78, while high-viscosity PET refers to products with IV > 0.78. This distinction reflects differences in molecular weight and corresponds to different applications and trade regulations.

For customs and trade purposes, PET products are also assigned different HS Codes. Low-IV PET is usually classified under HS Code 3907.61, mainly used for engineering plastics, films, and non-food packaging. High-viscosity PET typically falls under HS Code 3907.69, mainly for bottle-grade PET and food packaging production. Correct HS Code classification is crucial for exporters, as it directly affects tariffs, customs clearance procedures, and international pricing.

In trade practice, intrinsic viscosity is not only a technical parameter but also a key reference for pricing and contracts. Low-IV PET generally exhibits higher flowability, easier processing, and broader application, often corresponding to a lower price range. High-IV PET offers superior mechanical strength and thermal stability, targeting bottle-grade and food packaging markets, typically with higher prices. Clearly specifying the IV value and corresponding HS Code in contracts helps prevent trade disputes and improves transaction efficiency.

Comparison of Low- and High-IV PET Applications

Low-IV PET (IV ≤ 0.78) has a relatively lower molecular weight, resulting in higher melt flow and greater processing flexibility. It is commonly used in engineering plastic blends, photovoltaic films, and injection-molded components. Its excellent flowability allows it to fill complex molds easily, though its mechanical strength and thermal resistance are comparatively limited. In practical terms, low-IV PET enables easier injection molding of intricate parts and composite materials.

By contrast, high-IV PET (IV > 0.78) features a higher molecular weight, offering enhanced mechanical strength, structural integrity, and thermal stability, but lower flowability. It is widely applied in bottle-grade PET, food packaging films, and polyester fiber production. High-IV PET ensures that products such as beverage and water bottles maintain their shape during transport and handling, and it is particularly suitable for stretch-blow molding and blow molding processes. Simply put, the firmness of a mineral water bottle is largely attributed to the use of high-IV PET.

Wankai PET Resin Portfolio and Applications

Wankai New Materials specializes in the development and production of bottle-grade PET, with products featuring relatively high intrinsic viscosity (IV). These resins are widely used in beverage bottles, food containers, and pharmaceutical packaging. Different IV grades and material properties allow Wankai PET to serve not only bottle applications but also functional materials such as chemical fibers, BOPET films, and photovoltaic (PV) films.

Bottle-Grade PET (IV ≥ 0.76)

Wankai Brand PET has a higher molecular weight, providing superior mechanical strength and thermal stability. It is ideal for blow molding and stretch processes, ensuring bottles retain their shape during transport and use. Typical products include:

• WK-801: IV 0.80 ± 0.015 – water bottles, snack bottles, cosmetic bottles
• WK-801L: IV 0.77 ± 0.015 – similar to WK-801
• WK-811: IV 0.79 ± 0.015 – tea bottles, seasoning bottles
• WK-811L: IV 0.76 ± 0.015 – similar to WK-811
• WK-821: IV 0.83 ± 0.015 – edible oil bottles, pharmaceutical bottles
• WK-781: IV 0.78 ± 0.015 – transparent containers

Premium high-IV PET:

• WK-851: IV 0.88 ± 0.015 – carbonated beverage bottles, fast reheat
• WK-881: IV 0.87 ± 0.015 – carbonated beverage bottles
• WK-901: IV 0.87 ± 0.015 – large-capacity bottles

These three premium grades feature long polymer chains and high mechanical strength, making them especially suitable for high-pressure, high-load bottle applications. In simple terms, higher IV corresponds to a  "firmer" bottle that resists deformation.

Low-IV and Functional PET (IV ≤ 0.72)

Low-IV PET has smaller molecular weight and higher melt flow, making it suitable for injection molding, blending modifications, and film production. It serves as the base material for high-IV bottle-grade PET and functional films. Typical products include:

• WK-601: IV 0.60 ± 0.02 – base PET for WK-801 / WK-801L
• WK-611: IV 0.60 ± 0.02 – base PET for WK-811 / WK-811L
• WK-621: IV 0.60 ± 0.02 – base PET for WK-821
• WK-681: IV 0.645 ± 0.01 – PV films
• WK-711: IV 0.720 ± 0.015 – enhanced films, PV films
• WK-631: IV 0.645 ± 0.010 – BOPET films and filament yarns

Summary

Intrinsic viscosity (IV) is a critical parameter determining the molecular weight, mechanical performance, and processability of PET. It directly influences how PET flows during processing, its suitability for injection molding, blow molding, or film production, and the structural integrity of finished products. From functional films and fibers to beverage, food, and pharmaceutical packaging, Wankai PET supports a wide range of applications while maintaining reliability in both production and global trade.