Most kraft purchase orders start with two numbers: grammage and burst factor. Both matter, but they are not enough on their own. A grade that meets its GSM and BF on paper can still break on a corrugator, warp in a humid warehouse or fail a box compression test. This guide lists the parameters worth agreeing with any supplier before the first reel is made.
Grammage (GSM)
Grammage is the mass of one square metre of paper, in grams. It sets cost and the starting point for strength, so it should be stated with a tolerance rather than as a single figure. Ask how it is measured and how often.
Burst factor (BF)
Burst factor is bursting strength divided by grammage. It lets you compare the strength of grades of different weights. For recycled grades it depends heavily on the recovered fibre going into the pulper, which is why consistent grading of raw material matters to you as a buyer.
Moisture
Paper that is too dry cracks at the score lines; paper that is too wet loses stiffness and can warp. Agree an acceptable moisture range and ask how reels are protected in transit and storage.
Water absorption (Cobb)
The Cobb test measures how much water a known area of paper absorbs in a set time. It matters for boxes that see cold chains, humid climates or glue lines, and for any grade that is printed or laminated.
Reel geometry
State reel width, outer diameter, core inner diameter and the maximum number of joins per reel. A reel that does not fit your unwind stand or arrives with too many splices costs more on your line than the price difference between grades.
A short specification checklist
- Grade and intended use (liner, flute, wrapping, tube)
- GSM with tolerance
- Burst factor with tolerance
- Moisture range
- Cobb value, if the box sees moisture or print
- Reel width, diameter, core size and joins
- Monthly volume and delivery pattern
Send that list with your enquiry and a supplier can tell you quickly whether a grade fits, and what it will take to make it consistently.
Questions
What is BF in kraft paper?
BF, or burst factor, is the bursting strength of the paper divided by its grammage. It is the usual way Indian corrugators express how strong a kraft grade is relative to its weight.
What is a Cobb value?
The Cobb value is the mass of water a known area of paper absorbs in a set time, in grams per square metre. A lower value means the paper resists water better.
Grammage (GSM): what should buyers know?
Grammage is the mass of one square metre of paper, in grams. It sets cost and the starting point for strength, so it should be stated with a tolerance rather than as a single figure. Ask how it is measured and how often.
Burst factor (BF): what should buyers know?
Burst factor is bursting strength divided by grammage. It lets you compare the strength of grades of different weights. For recycled grades it depends heavily on the recovered fibre going into the pulper, which is why consistent grading of raw material matters to you as a buyer.
Moisture: what should buyers know?
Paper that is too dry cracks at the score lines; paper that is too wet loses stiffness and can warp. Agree an acceptable moisture range and ask how reels are protected in transit and storage.
Water absorption (Cobb): what should buyers know?
The Cobb test measures how much water a known area of paper absorbs in a set time. It matters for boxes that see cold chains, humid climates or glue lines, and for any grade that is printed or laminated.
Reel geometry: what should buyers know?
State reel width, outer diameter, core inner diameter and the maximum number of joins per reel. A reel that does not fit your unwind stand or arrives with too many splices costs more on your line than the price difference between grades.
A short specification checklist: what should buyers know?
Grade and intended use (liner, flute, wrapping, tube)GSM with toleranceBurst factor with toleranceMoisture rangeCobb value, if the box sees moisture or printReel width, diameter, core size and joinsMonthly volume and delivery pattern
Bollant Industries · Published 2026-10-20
