What is IV in PET Sheet and Why It Matters?

  • Post published:20/03/2026

Introduction

If you’ve been sourcing PET sheet for thermoforming, you’ve probably seen the term IV (Intrinsic Viscosity) on datasheets. Many buyers overlook it—but after 15 years in thermoforming materials, I can tell you:

IV is one of the most critical factors affecting forming stability, strength, and final product quality.

What is IV in PET Sheet?

Intrinsic Viscosity (IV) is a measure of the molecular weight of PET resin.

  • Higher IV → longer polymer chains
  • Lower IV → shorter chains

👉 In simple terms:
IV determines how “strong” and “stretchable” the material is during thermoforming.

IV

Typical IV Ranges for PET Sheet

ApplicationRecommended IV
Blister packaging0.72 – 0.78
Food containers0.75 – 0.82
Heavy-duty trays0.80 – 0.85

Why IV Matters in Thermoforming

📦
Forming Stability
Higher IV = better shape retention, less thinning
🔧
Mechanical Strength
Improved impact resistance & durability
💡
Transparency
Balanced clarity with proper IV level

Common Mistakes Buyers Make

❌ Choosing lowest price → often lowest IV
❌ Ignoring IV variation between batches
❌ Not matching IV to forming depth

How to Choose the Right IV (Procurement Guide)

When selecting PET sheet, ask:

  • What is the forming depth?
  • Is strength or clarity more important?
  • Is it APET or RPET?

👉 Quick rule:

  • Shallow forming → lower IV acceptable
  • Deep forming → higher IV required

Pro Tip from 15 Years Experience

If your forming line has unstable heating or inconsistent molds,
👉 choose slightly higher IV to compensate.

FAQ

  1. Q1: Is higher IV always better?

    No. Too high IV increases cost and may reduce processability.

  2. Q2: Does RPET have lower IV?

    Generally yes, but high-quality RPET can match virgin PET.

  3. Q3: Can IV affect cycle time?

    Yes. Higher IV may require slightly higher forming temperature.

Conclusion

IV is not just a number—it directly impacts:

  • forming success
  • product strength
  • production efficiency

👉 Ignoring IV is one of the most expensive mistakes in PET sheet sourcing.