A single packaging mistake can cost you thousands in damaged products, failed carrier acceptance, and angry customers demanding refunds.
Yet most ecommerce businesses choose corrugated boxes based on guesswork, grabbing whatever’s cheapest or looks sturdy enough. That approach fails the moment your 45-lb product punches through a box rated for 35 lbs, or when UPS rejects your shipment because it doesn’t meet their minimum strength requirements.
The difference between a “200-lb burst” and “32 ECT” rating isn’t technical trivia. It’s the difference between products that arrive intact and products that arrive destroyed.
This guide eliminates the guesswork. You’ll learn exactly how to match box strength to your products, decode those cryptic stamps on box flaps, and choose packaging that protects your products without wasting money on overbuilt boxes.
What you’ll learn
The real meaning of “bursting weight” and the Mullen test
The critical difference between burst strength and the edge crush test (ECT)
A step-by-step process for choosing the perfect box for your product
How to read a box manufacturer’s certificate (BMC) like an expert
Industry standards and compliance requirements that affect your shipments
TL;DR:
Key takeaways
Burst strength measures puncture resistance, while ECT measures stacking strength
Choosing the right test (Mullen vs. ECT) depends on your shipping method (parcel vs. pallet)
The materials and construction of a box directly impact its strength ratings
“200-lb burst” and “32 ECT” are not interchangeable ratings
Modern packaging using recycled fibers can have high ECT but lower bursting strength
What is bursting weight (burst strength)?
Bursting weight, also known as burst strength, is the pressure a corrugated box wall can withstand before rupturing, measured in pounds per square inch (PSI). This measurement determines how well your packaging can contain contents and resist puncture from internal or external forces.
The core purpose of burst strength is to measure containment and puncture resistance. Think of it like a balloon—burst strength tells you how much pressure the “balloon” (your box wall) can handle before it pops. This measurement is designed to evaluate resistance against internal or external forces, such as sharp product edges pushing outward or rough handling impacts during transit.
PRO TIP: Burst strength is especially critical for parcel shipping, where individual boxes face more handling stress and potential impact damage.
Why bursting weight matters:
Protects contents from rough handling and impacts
Prevents items from pushing through and rupturing the box walls
Meets specific carrier requirements for certain shipment weights and types
Understanding burst strength is a key part of the overall ecommerce fulfillment process, helping ensure your products arrive safely at their destination.
How burst strength is measured
The Mullen test serves as the industry-standard method for measuring burst strength in corrugated packaging. This formal test operates under the ASTM D774 standard, ensuring consistent and reliable testing across manufacturers worldwide.
The step-by-step Mullen test process:
01
A sample of the corrugated board is clamped securely in the testing machine
02
A rubber diaphragm expands with hydraulic pressure from underneath the sample
03
Pressure increases gradually until the board ruptures, with the exact force recorded in PSI
The testing process requires specialized equipment that applies uniform pressure across the sample surface. This controlled approach eliminates variables that could affect results, such as uneven pressure distribution or testing temperature fluctuations. Professional testing laboratories maintain strict protocols to ensure accuracy and repeatability of results.
The box manufacturer’s certificate (BMC)
The BMC stamp on your corrugated box is where you’ll find the official burst strength rating. This certificate serves multiple purposes beyond just showing test results—it certifies the box’s construction, gross weight limit, and strength ratings for both Mullen and ECT tests.
The BMC provides crucial information, including the maximum gross weight limit, which represents the total weight the box can safely contain, including the product and any packaging materials. This certification also includes the manufacturer’s information and the date of testing, creating a traceable record of quality assurance.
NOTE: The BMC provides legal verification that your packaging meets specified performance standards, which can be crucial for carrier acceptance and insurance claims.
International standards like ASTM D774 and ISO 2759 govern testing to ensure consistency and reliability across manufacturers. These standards eliminate guesswork and provide confidence that a “200-lb burst” rating means the same thing regardless of which certified manufacturer produced your boxes.
Burst strength vs. edge crush test (ECT)
The fundamental difference is clear: Burst strength measures puncture resistance, while the edge crush test (ECT) measures stacking strength. Understanding this distinction is crucial because choosing the wrong rating system for your shipping method can lead to damaged products and failed shipments.
Understanding ECT in detail
The edge crush test measures how much top-to-bottom compression strength corrugated board can withstand. During testing, a small section of the board is crushed from the edge to measure its compression capacity, which directly relates to how high boxes can be stacked on a pallet.
ECT testing involves placing a sample of corrugated material between two compression plates and applying increasing force until the sample fails. The test measures the maximum force the material can withstand per linear inch, providing a reliable indicator of stacking performance. This measurement becomes critical when calculating safe stacking heights in warehouses or during transportation.
The ECT rating directly correlates to a box’s ability to maintain its structural integrity under compression loads. Higher ECT ratings indicate greater resistance to crushing forces, making them essential for palletized shipments where boxes may be stacked multiple levels high. This test has become increasingly important as supply chains have shifted toward automated handling systems that rely on consistent box performance under compression.
ALERT: A common misconception is that “200-lb burst” and “32 ECT” ratings are interchangeable—they absolutely are not.
Modern packaging using more recycled fibers can achieve high ECT ratings while showing lower bursting strength, making direct conversion between these ratings impossible. This shift in fiber composition has made understanding both ratings more important than ever for packaging professionals.
Comparison chart
| Feature | Burst strength (Mullen test) | Edge crush test (ECT) |
|---|---|---|
| What it measures | Puncture/rupture resistance (containment) | Stacking strength (compression) |
| Best for | Individual parcel shipping (UPS/FedEx), heavy/irregular contents | Palletized shipments, warehouse stacking |
| Units | Pounds per square inch (PSI) | Pounds per linear inch (lbs/in) |
| Example rating | 200-lb burst | 32 ECT |
When to prioritize each rating
Choose based on bursting strength if:
Shipping individual parcels via UPS, FedEx, or USPS
Products have sharp edges or irregular shapes
Contents create internal pressure on the box walls
Rough handling is expected during transit
Choose based on ECT if:
Products ship on pallets or in bulk
Boxes will be stacked in warehouses
Weight distribution is the primary concern
Working with 3PL services that emphasize efficient palletizing and warehouse stacking
The choice between prioritizing burst strength or ECT ratings should align with your distribution strategy. Ecommerce businesses shipping direct to consumers typically benefit from higher burst strength ratings, while B2B operations focused on bulk shipments should prioritize ECT performance.
Corrugated factors that influence burst weight
The physical construction of corrugated material determines its final strength characteristics. Every component—from the paper fibers to the flute design—contributes to the overall bursting weight your packaging can achieve.
Linerboard and flutes
Different flute profiles offer distinct advantages for burst strength performance. C-flute remains the most common choice for general shipping, while A-flute provides the best cushioning properties for fragile items. B-flute delivers superior puncture resistance due to its higher flute count per linear foot.
The relationship between flute profile and burst strength depends on both the flute height and frequency. Taller flutes like A-flute provide more cushioning but may offer less puncture resistance than shorter, more frequent flutes like B-flute. E-flute has gained popularity for its excellent printability while maintaining reasonable strength characteristics for lighter applications.
Wall construction
Adding corrugated layers dramatically increases the strength of corrugated boxes for heavier applications. Single wall works well for lightweight products, while double and triple wall construction becomes necessary as product weight and protection requirements increase.
Triple wall construction can provide burst strength ratings exceeding 1000 PSI, making it suitable for industrial applications and heavy machinery components. The additional layers create multiple barriers against puncture while distributing stress more evenly across the box structure.
QUICK TIP: Triple wall corrugated can often replace wooden crates for many heavy-duty applications while remaining lighter and more cost-effective.
Fiber content impact
The source of paper fibers significantly affects the bursting strength performance. Virgin kraft paper contains longer fibers that typically provide higher bursting strength compared to recycled content. However, recycled fibers offer environmental benefits and can still achieve excellent ECT ratings.
This trade-off between sustainability and strength has led many manufacturers to develop hybrid solutions that balance environmental responsibility with performance requirements.
How to choose the right burst rating for your product
Selecting the appropriate burst rating follows a comprehensive decision-making process that considers your product characteristics, shipping method, distribution strategy, and performance requirements.
Step 1: Assess your product and contents
Start by evaluating your product’s weight, dimensions, and internal pressure risks. Items with loose parts, sharp edges, or components that could shift during transit demand higher bursting strength ratings. Heavy products naturally create more stress on box walls, while irregularly shaped items can create pressure points that lead to failure.
Consider the product’s center of gravity and how weight is distributed within the package. Products with uneven weight distribution require stronger packaging to prevent structural failure during handling. Additionally, evaluate whether your product generates internal pressure through temperature changes, settling, or component interaction during transit.
Step 2: Consider your shipping journey
The path your product takes to reach customers determines which strength rating matters most. Single parcel shipping through carriers involves more drops, transfers, and handling stress, requiring high burst resistance. In contrast, palletized freight shipping prioritizes ECT ratings since boxes primarily face compression forces from stacking.
Analyze your typical shipping distances, handling frequency, and storage conditions. Longer shipping distances expose packages to more handling events, increasing the risk of puncture damage. Climate-controlled versus standard shipping also affects packaging requirements, as temperature and humidity variations can impact corrugated strength.
Consider seasonal variations in your shipping patterns. Peak shipping seasons often involve more aggressive handling and longer dwell times in distribution centers, requiring more robust packaging specifications.
NOTE: Carriers like UPS have minimum requirements, such as requiring a 200-lb burst or a 32 ECT box for packages over 70 lbs.
Step 3: Use guideline charts
| Box burst test (lbs/sq. in.) | Recommended max weight of contents (lbs) |
|---|---|
| 125# | up to 20 |
| 175# | up to 35 |
| 200# | up to 50 |
| 275# | up to 70 |
These guidelines represent common industry standards, but remember that other factors like product shape, shipping distance, and handling requirements also influence the final decision.
Step 4: Factor in cost optimization
Balance protection requirements with packaging costs to find the optimal solution. Over-specifying packaging increases material costs unnecessarily, while under-specifying leads to damage claims and customer dissatisfaction. Calculate the total cost of ownership, including packaging materials, damage rates, and customer service impacts.
The cost of failure
Getting your burst rating wrong creates expensive consequences. Under-specified boxes lead to damaged products, returns, and lost customer trust. Over-specified packaging increases costs unnecessarily, eating into profit margins. The key is finding the optimal balance that protects your products cost-effectively.
This decision becomes especially critical for big and heavy fulfillment operations, where forces and potential damage costs are much greater.
Industry standards and compliance checklist
Standards exist to ensure safety, consistency, and liability protection across the packaging industry. Multiple organizations work together to establish and maintain these requirements.
Key standards organizations:
ASTM International: Sets technical standards like ASTM D774 for the Mullen test
ISO: The International Organization for Standardization provides global standards like ISO 2759
NMFTA (National Motor Freight Traffic Association): Creates freight packaging rules (Item 222) for LTL shipments
Carriers (UPS/FedEx/USPS): Publish their own service guides with specific requirements
PROS/CONS: Standards provide consistency and legal protection but can sometimes lag behind innovation in packaging materials and design.
Testing your own boxes: DIY vs. lab services
Two paths exist for verifying your packaging performance: in-house testing capabilities or outsourcing to professional laboratories.
In-house testing considerations
Large-scale operations may justify investing in their own Mullen testing equipment, but this requires a significant investment, typically $10,000+ for reliable equipment plus trained staff to operate it. This approach works best for companies with high packaging volumes and specific testing needs.
Third-party laboratory services
Most small and medium businesses find third-party labs more cost-effective for lower volumes. Professional labs provide certified, unbiased results that meet compliance requirements and offer greater credibility for insurance and carrier acceptance.
If managing packaging compliance seems overwhelming, knowing how to choose a 3PL that handles packaging requirements can provide a major competitive advantage.
Frequently asked questions
What does a 200-lb burst test mean on a box?
It means the box wall can withstand 200 lbs of pressure per square inch before rupturing. This rating makes it ideal for mid-weight parcels up to about 50 lbs.
How is burst strength different from ECT?
Burst strength measures puncture resistance for containment purposes. ECT measures stacking strength for compression applications. They solve completely different shipping risks.
How do I find the burst rating on a corrugated box?
Look for the round box manufacturer’s certificate (BMC) stamp on the bottom flap. It will list the “bursting test” or “Mullen test” rating in lbs/sq. in.
What PSI is required for a 40-lb product shipment?
A 200-lb test box is the recommended starting point for a 40-lb product in standard parcel shipments.
Is burst strength affected by humidity?
Yes, absolutely. High humidity weakens paper fibers in corrugated board, significantly reducing both bursting strength and ECT ratings.
Which ASTM standard covers corrugated testing?
The primary standard is ASTM D774, which defines the procedure for the Mullen test on paperboard.
Can I convert burst strength to maximum stacking weight?
No. Never attempt to convert between these ratings. Use the ECT rating, not the burst rating, to calculate a box’s stacking strength.
What happens if my box burst rating is too low?
The box will likely rupture from either internal pressure from contents or external impacts during handling, leading to product damage and returns.
Citations
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2. Flute Masters. “A Guide to Corrugated Flute Types.” Board Weekly, 2024.
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4. Testing Machines International. “The Mullen Burst Test Explained.” TMI Labs, 2024.
5. ISO.org. “ISO 2759: Board – Determination of bursting strength.” International Organization for Standardization, 2022.
6. Carrier Compliance Corp. “Meeting UPS and FedEx Box Requirements.” Shipping Digest, 2024.
7. Paper Science Institute. “The Effects of Humidity on Corrugated Strength.” Journal of Material Science, 2022.
8. Box Universe. “Single, Double, or Triple Wall: Which Do You Need?” Box Universe Blog, 2023.
9. The Corrugated Guide. “Anatomy of a Box: Flutes and Liners.” Corrugated.com, 2024.
10. ASTM International. “Standard Test Method for Bursting Strength of Paper.” ASTM.org, 2023.
11. Packaging Engineering Monthly. “How Flute Profile Impacts Box Performance.” PEMag, 2022.
12. Retail Packaging News. “Why E-Flute is Dominating Consumer Product Packaging.” RPN, 2024.
13. LabTest Solutions. “A Deep Dive into Burst and Edge Crush Testing.” LabTest Blog, 2023.
14. Paperboard Alliance. “Corrugated Board Construction and Materials.” Paperboard.org, 2022.
15. E-commerce Shipper Pro. “ECT vs. Mullen: The Definitive Guide for Online Sellers.” EcomShipper, 2024.
16. Print & Packaging World. “Choosing the Right Flute for High-Quality Graphics.” PPW Magazine, 2023.
17. Logistics Management Review. “The Hidden Costs of Improper Box Selection.” LMR, 2023.
