Why Thickness Tolerance Matters in Blister Packaging Materials

Thickness is the most basic specification on any packaging film, and also one of the most frequent sources of production problems. Understanding how tolerances are defined — and how they are verified — helps buyers avoid line stoppages that trace back to material variation.

How Tolerances Are Specified

A film specification typically states a nominal thickness plus a tolerance, for example 250μm ± 5%. The tolerance applies across the full web width and along the roll length. Two points matter in practice:

• Absolute tolerance versus percentage. At 250μm, a 5% tolerance is ±12.5μm. For thin films, absolute tolerance figures are easier to verify.
• Point-to-point versus average. A film can meet an average thickness target while varying unacceptably across the width. Specifications should state whether the tolerance applies to individual measurement points or to a roll average.

For blister forming, point-to-point variation matters more than average thickness, because local thin spots form faster and can perforate.

Why It Affects Forming

During thermoforming, the sheet is heated until it softens and then drawn into the cavity by vacuum or pressure. Thickness determines how much material is available to stretch into the cavity shape.

Thin regions reach forming temperature sooner, stretch more, and produce a thinner cavity wall. The consequences are:

• Web perforation at the corners of deep cavities
• Inconsistent cavity depth, which affects tablet seating and appearance
• Seal variation, because a thinner land area conducts heat differently
• Higher reject rates and more frequent line adjustment

Deep cavities and fast line speeds amplify the effect, which is why tolerance requirements tighten as forming depth increases.

Typical Tolerance Ranges

Where a line runs deep cavities or high speed, narrower tolerances — ± 3% or better — are often justified. Discuss the requirement with your supplier at qualification rather than after a forming problem appears. Our standard blister PVC range is available across a range of tolerance options.

How to Verify

Thickness should be verified with a calibrated gauge at defined intervals across the web width, not at a single point. Gravimetric methods, which weigh a defined area, are more accurate for thin films but slower.

Ask your supplier:

• What measurement method and interval is used for release testing
• Whether point-to-point data is available with the batch
• How tolerance is controlled at the edges, where variation is typically highest

Practical Takeaway

When a forming problem appears, thickness variation should be among the first things checked. If the material is within specification but at the edge of tolerance, tightening the specification is usually more effective than adjusting machine parameters — contact us to discuss tolerance requirements for your line.