Packaging Seal Peel Testing: Standards, Methods, and Best Practices

Packaging seal peel testing is a fundamental quality control and validation method that measures the force required to separate a sealed seam in flexible packages, sterile barrier systems, and laminated materials. Conducted in accordance with ASTM F88/F88M, ISO 11607, and EN 868, this test helps manufacturers quantify seal strength, analyze failure modes, validate sealing processes, and demonstrate regulatory compliance across the medical, pharmaceutical, and food packaging industries.

Technical Overview

Seal peel testing, also referred to as seal strength testing or peel force testing, quantifies the mechanical force required to pull apart the sealed edges of a package or the bonded layers of a laminated material. A universal testing machine (UTM) fitted with appropriate grips and support fixtures peels the seal apart at a controlled rate while a load cell records the force profile. Results are expressed as force per unit width of the seal, most commonly in N/15 mm, N/25 mm, or lbf/in.

The test evaluates two equally important aspects of seal quality. First, it verifies that the seal is strong enough to survive distribution stresses such as vibration, compression, and pressure differentials. Second, for peelable or easy-open designs, it confirms that the seal opens cleanly and consistently without shattering, tearing, or delaminating. Both excessively weak seals and over-sealed, brittle seams are considered defects, which is why peel strength is typically paired with a documented failure mode analysis.

Seal peel testing is governed by a family of internationally recognized standards and their national adoptions:

• ASTM F88/F88M — Standard Test Method for Seal Strength of Flexible Barrier Materials
• ASTM F2029 — Standard Guide for Making Laboratory Seals for Determination of Seal Strength
• ASTM D4332 — Standard Practice for Conditioning Containers, Packages, or Packaging Components for Testing
• ISO 11607-1 and ISO 11607-2 — Packaging for terminally sterilized medical devices
• EN 868 series — Packaging materials and systems for medical devices to be sterilized
• GB/T 19633 — Chinese national adoption of ISO 11607
• YY/T 0681.2 — Chinese medical packaging industry standard for seal strength testing, technically aligned with ASTM F88

Testing Samples

Flexible Pouches and Bags

Sealed pouches made from film-to-film, Tyvek-to-film, or foil laminate combinations are the most frequently tested sample type. Specimens are die-cut from finished package seals or from laboratory-produced seals so that each specimen contains a uniform length of the seal across its width.

Thermoformed Trays and Lidding Films

Rigid or semi-rigid thermoformed trays sealed with porous or non-porous lidding are tested by cutting strips that include the flange seal. Care is taken to test the seal itself rather than the tray corner geometry, which can artificially inflate or depress the measured force.

Blister Packages

For blister cards, peel testing evaluates the bond between the lidding foil and the formed cavity material such as PVC, PVDC, or cyclic olefin copolymer. Results support both opening-force design targets and seal integrity requirements.

Flat Laboratory Seals

During material selection and process development, flat specimens are sealed on laboratory heat sealers following ASTM F2029 so that sealing temperature, pressure, and dwell time can be mapped against resulting peel strength before package designs are finalized.

Testing Items

A comprehensive seal peel test program typically reports the following parameters:

• Maximum peel force — the peak load recorded during separation of the seal, normalized to specimen width
• Average peel force — the mean force sustained across the sealed region, useful for evaluating peel uniformity and easy-open behavior
• Force-displacement curve characteristics — including plateau stability, stick-slip behavior, and initiation force
• Failure mode classification — adhesive failure, cohesive failure, laminate delamination, or substrate tear
• Seal uniformity — variability among specimens taken from different locations along the same seal and among multiple packages
• Comparative performance — seal strength before and after sterilization, transportation simulation, or accelerated aging

Testing Methods

Testing is performed on a calibrated universal testing machine with a suitable low-capacity load cell and pneumatic or mechanical grips. Specimens, typically 15 mm or 25 mm wide with sufficient tab length for gripping, are conditioned to a standard atmosphere of 23 ± 2 °C and 50 ± 5% relative humidity in accordance with ASTM D4332 before testing. A crosshead speed of 200 to 300 mm/min is commonly applied unless a product specification requires otherwise, and no fewer than five specimens per seal are recommended for statistical validity.

ASTM F88/F88M defines three fixture configurations, selected according to sample rigidity and the angle representative of real-world opening:

• Unsupported (manual 90° peel) — the operator holds the free tail by hand, suitable for flexible, compliant pouches
• Sliding supported 90° peel — a sliding platform supports the specimen to maintain a consistent 90° peel angle for semi-rigid samples
• Fixed constrained 180° peel — the specimen is bent back over a rigid flange so that the seal peels at 180°, typically used for stiffer laminates and tray lid combinations

During the test, force and displacement data are captured at a sufficient sampling rate to resolve peaks. The reported peel strength is calculated by normalizing the peak or average force to the specimen width. Immediately after separation, the failure surfaces are examined and the dominant failure mode is classified:

• Adhesive failure — clean separation at the seal interface, generally the intended mode for peelable seals
• Cohesive failure — rupture within the sealant layer, often accompanied by stringing or residue transfer
• Laminate delamination — separation between plies of a multilayer material, indicating the internal bond is weaker than the seal
• Substrate or material tear — the film or porous web tears before the seal releases, indicating the seal is stronger than the material itself

The final test report documents sample identification, specimen dimensions, conditioning history, fixture configuration, test speed, individual and statistical force values, and failure mode distribution, providing traceable objective evidence for design validation and process control.

Applications

Seal peel testing is applied throughout the packaging lifecycle across multiple regulated industries:

• Medical device packaging — seal strength validation of sterile barrier systems as required by ISO 11607, supporting installation, operational, and performance qualification of sealing processes
• Pharmaceutical packaging — verification of lidding-to-blister and pouch seal strength for unit-dose and combination products
• Food and beverage packaging — confirmation of seal performance for flexible bags, stand-up pouches, and retort applications
• Industrial and electronics packaging — evaluation of moisture barrier bags and protective laminated enclosures
• Process development and optimization — mapping heat seal temperature, dwell time, and pressure windows to establish robust sealing parameters
• Stability and shelf-life studies — measuring seal strength retention after sterilization cycles, accelerated aging, and transport simulation
• Ongoing quality control — periodic monitoring of production seals to detect tooling wear, parameter drift, or material lot variation

Many manufacturers supplement in-house capability by engaging accredited third-party laboratories for independent validation studies, method development, and regulatory submission support.

FAQ

What is the difference between seal strength and seal integrity?

Seal strength measures the mechanical force required to open a seal, while seal integrity verifies the absence of leaks or channels that could allow contamination. The two properties are complementary: a seal can be strong yet contain a microscopic channel, or uniform yet too weak for distribution. ISO 11607 expects both to be evaluated using appropriate test methods.

Why is failure mode analysis as important as the force value?

A high peel number caused by material tearing rather than controlled interfacial peeling may indicate an over-sealed package that opens unpredictably. Conversely, cohesive or delamination failure at acceptable force levels can signal long-term durability risks. Classifying the failure mode confirms that the package fails in the way the design intends.

How many specimens should be tested?

ASTM F88 recommends testing multiple specimens from each seal location, and validation programs typically require at least five to ten specimens per seal per package, sampled across multiple packages from representative production lots.

Are Tyvek and other porous materials tested differently?

They are tested with the same equipment, but specimen preparation matters more. Because porous webs can tear during gripping, adequate tab length and careful die-cutting are essential, and sliding 90° support fixtures are frequently used to maintain a stable peel angle.

What acceptance criteria should be applied?

There is no universal pass threshold. Manufacturers define minimum and, where applicable, maximum peel strength values based on a documented risk assessment, distribution testing, clinical or user opening requirements, and the performance limits of the chosen materials, then verify those limits through testing in accordance with ISO 11607.