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Understanding GSM, BF & ECT in Corrugated Packaging

5 min read · Asian Packaging Industries

What is BF (Burst Factor) in Corrugated Boxes?

When purchasing corrugated boxes, you may often hear terms such as 18 BF, 20 BF, 24 BF, 28 BF, or 35 BF. Many buyers assume that a higher BF automatically means a stronger box, but that’s only part of the story.

Burst Factor (BF) is one of the most important quality parameters used in the corrugated packaging industry. It measures the strength of paper and its ability to withstand pressure before bursting. Choosing the correct BF helps ensure your packaging can safely protect products during handling, storage, and transportation.

At Asian Packaging Industries, we carefully select paper grades based on the product, transportation conditions, and customer requirements. This guide explains everything you need to know about Burst Factor and why it plays a vital role in corrugated packaging.

What is Burst Factor (BF)?

Burst Factor (BF) is the measure of a paper’s resistance to rupture when pressure is applied perpendicular to its surface.

In simple words, it tells us how much pressure the paper can withstand before it bursts.

The higher the Burst Factor, the stronger the paper.

BF is one of the most commonly used parameters for selecting kraft paper used in manufacturing corrugated boxes.

Why is Burst Factor Important?

During transportation, corrugated boxes experience several types of stress:

Stacking pressure in warehouses
Compression during transport
Sudden impacts
Rough handling
Vibrations
External loads

Paper with an appropriate Burst Factor helps the corrugated box maintain its integrity under these conditions.

Using the correct BF reduces:

Box failure
Product damage
Customer complaints
Replacement costs
Transportation losses

How is Burst Factor Calculated?

Burst Factor is calculated using the following formula:

Burst Factor (BF) = Bursting Strength ÷ GSM

Where:

Bursting Strength = Pressure at which the paper bursts (measured in kg/cm²)
GSM = Grammage of the paper (grams per square metre)

Example

Suppose a kraft paper has:

GSM = 180
Bursting Strength = 360

Then:

BF = 360 ÷ 180 = 20 BF

This means the paper is classified as 20 BF.

Difference Between Bursting Strength and Burst Factor

Many people confuse these two terms.

Bursting Strength	Burst Factor
Actual pressure required to burst paper	Ratio of Bursting Strength to GSM
Measured during testing	Calculated value
Expressed in kg/cm²	Expressed as BF
Depends on paper quality	Helps compare papers of different GSM

Both values are important, but BF provides a standardized way to compare paper grades.

Common Burst Factor Grades

Different industries use different BF grades depending on the product and packaging requirements.

BF Grade	Typical Application
16 BF	Lightweight packaging
18 BF	General retail packaging
20 BF	FMCG and consumer goods
22 BF	Medium-duty cartons
24 BF	Industrial packaging
26 BF	Heavy products
28 BF	Export packaging
30 BF	Heavy engineering
35 BF	High-strength industrial packaging

The required BF depends on product weight, transportation distance, stacking conditions, and customer specifications.

How is Burst Factor Tested?

Burst Factor is determined using a Bursting Strength Tester.

Testing Process

A paper sample is placed between two circular clamps.
A rubber diaphragm applies hydraulic pressure.
Pressure increases gradually.
The pressure at which the paper bursts is recorded.
BF is calculated using the GSM of the paper.

The test follows recognized industry standards to ensure consistent and accurate results.

Factors That Affect Burst Factor

Several factors influence the BF of kraft paper.

Paper Quality

Virgin kraft paper generally offers higher BF than recycled paper.

Fibre Strength

Longer and stronger fibres improve bursting resistance.

Moisture Content

Excess moisture weakens paper and lowers Burst Factor.

Manufacturing Process

Proper refining, bonding, and quality control improve paper performance.

Storage Conditions

Improper storage in humid environments can reduce BF over time.

Does Higher BF Always Mean Better Packaging?

Not always.

Many buyers believe they should always choose the highest BF available. In reality, selecting an unnecessarily high BF can increase packaging costs without providing additional benefits.

Packaging performance depends on several factors, including:

GSM
Flute type
Ply construction
Edge Crush Test (ECT)
Box Compression Test (BCT)
Box design
Product weight

An optimized combination of these factors often performs better than simply increasing the BF.

Typical BF Selection Based on Products

18–20 BF

Suitable for:

Apparel
FMCG
Bakery products
Retail packaging
E-commerce

22–24 BF

Recommended for:

Pharmaceuticals
Consumer electronics
Food products
Household appliances
Industrial supplies

26–30 BF

Ideal for:

Engineering components
Automotive parts
Chemical products
Export cartons
Heavy consumer goods

35 BF and Above

Used for:

Heavy machinery
Industrial equipment
Export packaging
High-value products

Common Myths About BF

Myth 1: Higher BF Always Means Stronger Boxes

Not true.

Board construction, flute type, and box design are equally important.

Myth 2: BF and GSM Are the Same

No.

GSM measures paper weight.

BF measures paper strength.

Myth 3: 5 Ply Boxes Always Need High BF

Not necessarily.

The required BF depends on product weight and transportation conditions.

Myth 4: BF Alone Determines Box Quality

Incorrect.

Other important quality tests include:

Edge Crush Test (ECT)
Box Compression Test (BCT)
Cobb Test
Moisture Test
Grammage Test

All these parameters work together to determine packaging performance.

Expert Tips from Asian Packaging Industries

Choosing the correct Burst Factor requires balancing product protection and packaging cost.

Our recommendations:

✔ Use higher BF for heavy or export shipments.

✔ Combine the appropriate BF with the correct flute profile.

✔ Never select paper based only on GSM.

✔ Test packaging before mass production.

✔ Consult packaging experts for customized specifications.

These practices help reduce damage while keeping packaging economical.

Why Choose Asian Packaging Industries?

At Asian Packaging Industries, quality begins with selecting the right raw materials. Every corrugated box we manufacture is designed to meet the customer’s product requirements, transportation conditions, and industry standards.

Our strengths include:

Family-owned packaging business with decades of experience
Six advanced manufacturing units
Annual turnover of approximately ₹107+ crore
250+ skilled workforce supported by experienced technical staff
Imported Heidelberg 5-Colour + Coater printing technology
Automatic corrugation and converting lines
In-house quality testing for BF, GSM, ECT, and other parameters
Customized packaging solutions
Reliable transportation fleet for on-time deliveries

By combining quality materials, advanced technology, and rigorous testing, we ensure every corrugated box delivers reliable performance.

Frequently Asked Questions

What does 20 BF mean?

A 20 BF paper has a Burst Factor of 20, indicating its resistance to bursting pressure relative to its GSM. It is commonly used for consumer goods and general-purpose corrugated boxes.

Is BF more important than GSM?

Both are important. GSM indicates the weight of the paper, while BF measures its strength. A good packaging design considers both values together.

Which BF is suitable for export packaging?

Export cartons often use 24 BF, 28 BF, or higher, depending on the product weight, shipping method, and destination.

Can recycled paper have a high BF?

Yes, but virgin kraft paper generally achieves higher Burst Factors and more consistent performance.

Should I always choose the highest BF?

No. The ideal BF depends on your product and packaging requirements. Using a higher BF than necessary can increase costs without providing significant additional benefits.

Conclusion

Burst Factor is a critical parameter in determining the strength and durability of kraft paper used in corrugated packaging. It helps manufacturers and buyers select the right paper grade based on product weight, transportation conditions, and storage requirements. However, BF should never be evaluated in isolation. Factors such as GSM, flute type, board construction, and other quality tests all contribute to the overall performance of a corrugated box.

At Asian Packaging Industries, we combine technical expertise, quality raw materials, advanced manufacturing, and comprehensive testing to deliver packaging solutions that provide the right balance of strength, protection, and cost efficiency. Whether you need packaging for retail products, industrial components, or export shipments, our team can help you choose the ideal specification for your application.

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