BF and GSM in Corrugated Boxes Explained

GSM (Grams per Square Metre): Measures paper thickness and grammage. Higher GSM = heavier paper.
BF (Bursting Factor): Measures the intrinsic fiber tensile strength of paper independent of its weight.
Bursting Strength (BS): The actual hydrostatic pressure (in kg/cm²) the paper can withstand before rupturing.

The Indian Paper Trade Bursting Formula

In paper mills and packaging procurement throughout India, bursting strength is determined using this exact formula:

Bursting Strength (kg/cm²) = [ Bursting Factor (BF) × Grammage (GSM) ] ÷ 1,000

Example Calculation: If your carton is made from 150 GSM kraft paper with an 18 BF rating:

BS = (18 × 150) ÷ 1,000 = 2.70 kg/cm² per liner

If you upgrade the paper from 18 BF to 24 BF while maintaining the same 150 GSM weight:

BS = (24 × 150) ÷ 1,000 = 3.60 kg/cm² (a 33% increase in strength with zero added weight!)

Paper Grade	Typical GSM Range	Raw Material Source	Recommended Application
14 – 16 BF	100 – 140 GSM	Recycled Agro Waste / Waste Paper	Inner fluting medium, lightweight partitions.
18 – 20 BF	120 – 180 GSM	Semi-Chemical Kraft	Standard e-commerce mailers, FMCG retail outer cartons.
22 – 24 BF	140 – 220 GSM	Virgin Kraft Pulp Blends	Edible oil cartons, master transit shippers, export packaging.
28 – 32+ BF	180 – 300 GSM	100% Virgin Pine / Hardwood Kraft	7-ply heavy machinery boxes, automotive transmission crates.

Burst Factor (BF): Evaluates individual paper sheets before fluting.
Edge Crush Test (ECT): Evaluates the edgewise compressive strength of combined corrugated board (measured in kN/m or lbs/in). This dictates how much pallet weight the vertical box walls can support.
Box Compression Test (BCT): Evaluates the complete finished box under top-to-bottom compressive load in our laboratory test rig before failure.

TopWay's quality testing lab in Sitapura verifies BF, ECT, and Mullen Burst on every production run.