The Mullen Burst Test is a standardized procedure used to evaluate the strength and durability of packaging materials, primarily paperboard and corrugated fiberboard. This test provides a single, measurable value that represents a material’s resistance to rupture or puncture. Understanding this metric helps manufacturers and shippers select the appropriate container to ensure product protection throughout the supply chain. The Mullen test predicts how a container will perform when subjected to sudden, concentrated force during handling and transit.
What is the Mullen Burst Test?
This test specifically measures the force required to physically puncture or rupture a specific area of the corrugated material. The result is expressed in pounds per square inch (PSI), quantifying the material’s resilience against concentrated impact. This measurement simulates the kind of force that occurs when an object pushes against the box wall from the inside or the outside. High Mullen ratings are often selected for products where a failure of the box side wall, rather than compression from stacking, is the primary concern. The PSI value correlates to the material’s impact resistance and toughness, making it a reliable indicator of a container’s ability to protect contents during rough, individual parcel handling.
How Burst Strength is Measured
Measurement of burst strength is performed using a specialized apparatus called a Mullen Tester. A small, circular sample of the corrugated board is firmly clamped between two annular plates to prevent slippage during the test. The testing mechanism then applies increasing pressure to the underside of the clamped sample. This pressure is generated hydraulically, typically by forcing a liquid like glycerin against a circular rubber diaphragm positioned beneath the specimen. As the pressure builds, the diaphragm expands upward, pushing against the material until the fibers rupture. The machine records the maximum pressure, in PSI, achieved at the moment the material fails. Standardized procedures ensure consistent and repeatable results across the packaging industry.
Why Burst Strength is Important for Packaging
A high burst strength is a direct indication of a container’s ability to survive rough individual handling throughout the shipping process. Packages are frequently subjected to drops, impacts, and collisions on conveyor belts or during manual loading and unloading. The Mullen rating is a direct measure of how well the corrugated structure resists these sudden, non-uniform forces. This strength is particularly relevant for shipping products that are heavy, dense, or have sharp, protruding edges. A box with a high burst strength prevents both the internal contents from puncturing the box and external forces from penetrating the package wall.
Understanding Burst Strength Grades
Packaging materials are historically graded using standardized burst strength ratings, commonly referred to as the “Mullen test.” These grades are typically expressed as a weight value, such as 200-lb test or 275-lb test, corresponding to the minimum burst strength in pounds per square inch (PSI). For example, a box stamped with a 200-lb test rating is certified to withstand a minimum of 200 PSI of force before rupturing. These ratings were historically mandated by former carrier regulations, such as the railroad’s Rule 41 and the trucking industry’s Item 222, to govern the quality of packaging used for freight. The higher the grade number, the stronger the material, allowing manufacturers to quickly determine a box’s suitability for heavy or fragile contents.
Burst Test Versus Edge Crush Test
The Edge Crush Test (ECT) is the primary alternative to the Mullen Burst Test, and it measures a fundamentally different property of the corrugated board. While the Mullen test assesses puncture resistance, the ECT measures the material’s edgewise compressive strength, which is its resistance to a top-to-bottom crushing force. The ECT quantifies a box’s stacking stamina, expressed in pounds per linear inch (PLI), which is the force required to crush a sample standing on its edge.
The difference in focus reflects distinct priorities in modern logistics: Mullen is for individual package integrity, and ECT is for warehousing and palletizing efficiency. The industry has largely shifted toward ECT because most modern shipping involves stacking boxes on pallets for storage and transit, where vertical compression strength is the most significant factor.
ECT-rated materials often use less fiber to achieve sufficient stacking strength, which can result in cost savings and less material waste. However, the Mullen test retains its importance for products that are heavy, have sharp points, or are shipped in less-than-truckload (LTL) environments where packages face more unpredictable, rough handling and impact forces.