What Is Burst Strength in Package Integrity Testing?
What Is Burst Strength?
Burst strength is the maximum pressure (internal or external) a package or packaging component can withstand before structural failure — typically defined as the point where the package seal ruptures, the film bursts through, or the container wall fractures. It is a direct measure of the package’s structural resistance to pressure loading and is used to characterise seal quality, film or container material toughness, and overall package structural integrity.
Burst strength testing is a critical qualification and quality control method for flexible pouches, heat-sealed packaging, blow-moulded containers, and rigid packaging systems across the electronics, medical device, food, and specialty chemical packaging industries.
Why Burst Strength Testing Is Important
Seal Quality Indicator
In heat-sealed flexible packaging, burst strength directly reflects the quality of the heat seal — the combination of seal temperature, dwell time, pressure, and material compatibility. Weak seals (from incomplete fusion, contamination, or process deviation) fail at lower burst pressures than properly formed seals. Burst testing provides a rapid, sensitive indicator of seal process control.
Product Containment Assurance
Packages must maintain their containment integrity through pressure events encountered during distribution — altitude changes during air transport (described in Blog 83), accidental compression during stacking, and internal gas pressure from product off-gassing. Burst strength testing verifies adequate structural margin against these pressure loading events.
Sterile Barrier Integrity
For medical device sterile packaging (ISO 11607), burst strength testing of pouches and trays characterises the structural integrity of the sterile barrier. Combined with seal peel strength testing (ASTM F88) and integrity testing (ASTM F2338), burst testing provides comprehensive packaging system characterisation for regulatory submissions.
Burst Strength Test Methods
ASTM F1140 — Internal Pressurisation Failure Resistance of Unrestrained Packages
ASTM F1140 measures burst strength of flexible pouches and semi-rigid trays by internally pressurising the sealed package with air or inert gas at a defined rate until failure. The maximum pressure at burst (or seal peel initiation) is reported as the burst strength in kPa or psi.
The standard defines two test methods:
- Method A (Uniform Rate of Pressure Increase): Constant pressure increase rate until burst — measures peak burst pressure
- Method B (Constant Pressure Hold): Package is pressurised to a defined threshold and held — measures time to failure or confirms whether the package survives the proof pressure
ASTM F2054 — Burst Testing of Flexible Packaging Seals Using Internal Air Pressurization Within Restraining Plates
Uses rigid restraining plates on both faces of the flat packaging — limiting film deformation and focusing stress on the seal line rather than the film. This provides a purer measure of seal failure pressure independent of film extensibility.
ASTM D3786 — Hydraulic Bursting Strength of Textile Fabrics and Films
Hydraulic burst testing applies water pressure through a flexible diaphragm to the sample surface — measuring burst pressure for flexible films and coated fabrics where biaxial tensile stress resistance governs performance.
TAPPI T807 — Bursting Strength of Paper and Paperboard
Mullen burst test — measures pressure to burst paper and paperboard specimens using a rubber diaphragm pressed against the specimen — widely used for corrugated cardboard and paper packaging qualification.
Factors Affecting Burst Strength
Seal quality: Temperature, pressure, and dwell time during heat sealing. Film mechanical properties: Ultimate tensile strength and elongation of the packaging film. Package geometry: Larger seal area distributes pressure over more seal width, increasing burst resistance. Test temperature: Lower temperatures increase film stiffness and may produce higher burst pressures with brittle fracture rather than ductile peel failure.
Why Choose Infinita Lab for Burst Strength Testing?
Infinita Lab provides burst strength testing per ASTM F1140, ASTM F2054, and related standards for flexible and rigid packaging through our nationwide accredited packaging testing laboratory network.
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Frequently Asked Questions (FAQs)
What is the difference between burst strength and seal peel strength for flexible packaging? Seal peel strength (ASTM F88) measures the force per unit width to progressively peel a seal open at a defined angle — characterising seal cohesion under peel loading. Burst strength measures the maximum internal pressure the sealed package withstands before any failure — characterising resistance to distributed biaxial pressure loading. Both are needed for complete seal characterisation — they can rank seals differently because peel and burst loading modes engage different failure mechanisms.
What burst strength is typically required for medical device sterile packaging? ISO 11607 does not define minimum burst strength values — manufacturers must establish minimum acceptable limits through design validation testing correlated with distribution environment stresses and seal integrity requirements. Typical pharmaceutical pouch burst minimums range from 15–50 kPa depending on package size and contents. Minimum limits are established through worst-case distribution simulation (ASTM D4169 or ISTA testing) followed by burst testing.
Can burst strength be used to predict shelf life of sealed packages? Burst strength after accelerated ageing (elevated temperature and humidity storage per ASTM F1929 conditioning protocols) provides an indication of how seal quality changes over time. Packages that maintain burst strength above the minimum specification after accelerated ageing equivalent to the target shelf life pass the shelf life validation requirement.
What failure mode should be observed in ASTM F1140 burst testing? Seal failure (cohesive or adhesive) is the expected and desired failure mode — confirming that the seal is the limiting element. Film burst (failure through the packaging material, not the seal) indicates that the seal is stronger than the film — which may be desirable for very high-integrity seals but prevents direct seal quality characterisation from the burst test result.
How does package size affect burst strength results? Larger packages with the same seal width have lower burst pressure because the same internal pressure creates greater total force on the seal for larger package area. ASTM F1140 reports burst pressure in kPa — which is geometry-independent for comparing packages of different sizes. However, the force per unit seal width increases with package perimeter, so large packages inherently challenge seal integrity more than small packages at the same internal pressure.
