What Does BF Mean in Kraft Paper? 16, 18, 20 and 22 BF Explained
BF means burst factor. It is a kraft paper's bursting strength divided by its weight, so it rates strength per gram, not strength per sheet. Bursting strength in kg per sq cm is roughly BF times GSM divided by 1,000, so 150 GSM paper at 18 BF bursts at about 2.7. Higher BF means stronger fibre.
What does BF mean in kraft paper?
BF stands for burst factor. It is the bursting strength of a sheet of kraft paper divided by its grammage, the paper's weight in grams per square metre (GSM). Because it divides out the weight, BF tells you how strong the fibre is, gram for gram. Two papers can weigh the same and still differ in strength; BF is the number that shows it.
The trade formula, as test-equipment maker Presto Stantest sets it out, is BF equals bursting strength in kg per square centimetre, times 1,000, divided by GSM. Turn it around and you get the useful rule of thumb: bursting strength is roughly BF times GSM divided by 1,000. So a 150 GSM sheet at 18 BF bursts at about 2.7 kg per square centimetre, and the same 150 GSM sheet at 22 BF bursts at about 3.3.
BF is also written into an Indian Standard. IS 1397:1990, the kraft paper specification, defines burst factor as burst index times 10.2, where burst index is the lab measure in kPa square metres per gram. That standard covers wrapping kraft; the paper used to make corrugated board, liner and fluting medium, has its own standard, IS 9588:2025. Modern labs usually report burst index rather than BF, and PaperIndex Academy notes that BF mixes units and is not part of current ISO standards. In Indian box buying, though, BF is still the grade name you will hear.
GSM is how heavy the paper is. BF is how strong each gram of it is.
What do 16, 18, 20 and 22 BF mean?
The number is the burst factor itself, so a higher number means a stronger sheet at the same weight. Indian corrugating paper is bought in bands rather than a fixed ladder of grades. An IPPTA industry presentation on Indian corrugated raw material shows production split across these bands, and notes that the paper is specified by just two numbers: burst factor and substance (GSM).
| BF band | Share of production | Burst at 150 GSM (rule of thumb) |
|---|---|---|
| 12 to 16 BF | 15% | about 1.8 to 2.4 kg per sq cm |
| 18 to 20 BF | 50% | about 2.7 to 3.0 kg per sq cm |
| 22 to 24 BF | 15% | about 3.3 to 3.6 kg per sq cm |
| 28 to 35 BF | 20% | about 4.2 to 5.3 kg per sq cm |
So 16, 18, 20 and 22 BF are common points inside those bands, not separate standard grades. The burst column is our arithmetic from the rule of thumb above, for a single sheet of paper, not for finished board. The 18 to 20 BF band is the workhorse, half of all production.
Which BF do I need for 3, 5 and 7 ply?
There is no fixed BF for a ply count. Ply decides how many layers of paper the board has; BF decides how strong each layer is. The right BF comes from the load and the stack, not from the ply number. Presto's buyer guide puts it simply: about 16 BF for lightweight boxes, 18 BF for normal packaging, and 24 BF or higher for heavy products.
- Light parcels, single units, short courier routes: a lower BF in 3 ply usually carries the load.
- Everyday shipping cartons stacked a few high: the 18 to 20 BF band is the common choice.
- Heavy, dense or export loads stacked deep: higher BF liners, often with 5 or 7 ply.
- Boxes that sit at the bottom of a tall stack for weeks: specify on stacking strength, then pick BF and ply to meet it.
We work across the common BF grades and choose the BF for your load and stacking needs. Tell us what goes in the box, its weight and how high the cartons stack, and the spec follows from that. For the GSM side of the same decision, our board GSM guide sets out typical board weights by ply.
Does higher BF cost more?
Yes. Kraft paper is priced by BF; the IPPTA presentation states it plainly: pricing is based on burst factor. Stronger fibre needs better or more virgin input, so a higher BF sheet usually costs more per kg than a lower BF sheet of the same weight.
Prices also move by region and by week, so read any single number with its date. On 2 October 2026, The Pulp and Paper Times reported North India 18 BF basic kraft at about Rs 36 per kg, Gujarat 16 BF at about Rs 37 and Chennai 18 BF at about Rs 38. Those are regional prices on one date, not a BF price ladder; our October Kraft Ledger tracks how they moved.
For your box, what matters is the effect per piece. Our estimate from the quote engine: every Rs 1 per kg on the paper rate moves a 3 ply 12 x 10 x 6 inch box by about Rs 0.31 to Rs 0.36 at 5,000 boxes. A higher BF that lets you drop a ply or cut GSM can save more than the BF premium costs.
BF vs GSM: which matters for box strength?
Both, because bursting strength is the product of the two. A heavier sheet at low BF and a lighter sheet at high BF can burst at the same pressure. That is why a quote that lists only GSM, or only BF, tells you half the story. Ask for both on the same line.
Burst is not the whole picture. The same IPPTA presentation cautions that burst does not reliably predict how board behaves in edge crush or compression, and notes buyers shifting to specifying boxes by box compression (BCT) and edge crush (ECT). If your boxes stack, read our guide to box strength tests next.
Ask for GSM and BF on the same line of the quote. One without the other is half a spec.
Board is GSM-checked and burst-tested, and you can ask for a test on your order. You approve a physical sample before any run. Our minimum order is 5,000 boxes, or 1,000 for larger sizes, and boxes are ready in 5 to 7 days after sample and artwork approval, ex-factory.
Frequently asked questions
What is a good BF for a shipping box?
For everyday shipping cartons the 18 to 20 BF band is the common choice, and it makes up about half of Indian corrugating paper production. Light parcels can use a lower BF, and heavy or deeply stacked loads need a higher one. We choose the BF for your load and stacking needs.
Is 18 BF the same as 18 GSM?
No. GSM is the weight of the paper in grams per square metre. BF is its bursting strength divided by that weight. An 18 BF paper can come in many weights, such as 120, 150 or 180 GSM, and its bursting strength rises with the weight.
Can I ask for a specific BF?
Yes. Tell us the BF and GSM your spec calls for, or tell us the load and stack height and we will choose them. We work across the common BF grades. Board is GSM-checked and burst-tested, and you can ask for a test on your order.
Is BF in an Indian Standard?
Yes. IS 1397:1990, the kraft paper specification, defines burst factor as burst index times 10.2. Paper for corrugated board is covered by IS 9588:2025, kraft liner and corrugating medium. Labs often report burst index; the Indian box trade still names paper by BF.