Fiber Furnish Calculator
Design a paper fiber blend from softwood kraft, hardwood kraft, mechanical, and recycled pulp. Predict strength, formation, opacity, freeness, and fiber cost.
About this calculator
This calculator blends four pulp furnish types — softwood kraft, hardwood kraft, mechanical (TMP/groundwood), and recycled/deinked — into predicted paper properties using simple weighted averages, first normalizing whatever percentages you enter to sum to 100% so the math still works if your inputs don't add up exactly. Each fiber type carries a fixed coefficient on a 0-100 scale for five properties: softwood kraft's long fibers dominate tensile (95) and tear (100) strength, hardwood kraft's short fibers score highest on formation quality (90) reflecting the sheet-uniformity benefit short fibers give, and mechanical pulp tops opacity (95) at the cost of the lowest strength numbers. The blend is a straight linear combination of your normalized percentages against those per-type coefficients, so it captures directional trade-offs (more mechanical pulp buys opacity and cost savings but costs you tensile and tear) without modeling any real fiber-to-fiber interaction, refining variables, or furnish-specific freeness behavior.
Freeness (CSF) is estimated the same way, from typical drainage-rate coefficients per fiber type, and fiber cost per ton uses flat reference prices ($800/700/400/300 per ton for softwood kraft/hardwood kraft/mechanical/recycled respectively) that will drift from your actual supplier pricing. Treat every output as a directional index for comparing furnish recipes against each other, not as a lab strength-testing substitute — real tensile, tear, and burst values depend on refining, additives, and machine conditions this model doesn't include.
Inputs
Results
Tensile index (0-100)
68
How to Use This Calculator
- Enter the percentage of each fiber type — softwood kraft, hardwood kraft, mechanical, and recycled (values are auto-normalized to 100%).
- Input your target paper weight in GSM.
- Review predicted strength indices: Tensile Index, Tear Index, Burst Index.
- Check Formation Index and Opacity Index to assess printability.
- Use Freeness (CSF ml) and Fiber Cost per Ton to optimize drainage and economics.
How the result changes with Softwood kraft (%)
| Softwood kraft (%) | Tensile index (0-100) |
|---|---|
| 15 | 63.2 |
| 23 | 66 |
| 45 | 71.5 |
| 75 | 76.4 |
What each input means
- Softwood kraft (%)
- Long-fiber softwood kraft pulp percentage. High strength, good tear resistance.
- Hardwood kraft (%)
- Short-fiber hardwood kraft pulp. Better formation, smoothness, and printability.
- Mechanical pulp (%)
- TMP or groundwood mechanical pulp. High opacity, low cost, lower strength.
- Recycled fiber (%)
- Deinked recycled fiber. Cost-effective but variable quality.
- Target paper GSM
- Target paper weight in grams per square meter.
What each result means
- Tensile index (0-100)
- Predicted tensile strength index (higher = stronger).
- Tear index (0-100)
- Predicted tear resistance index.
- Burst index (0-100)
- Predicted burst strength index.
- Formation (0-100)
- Sheet formation quality (higher = more uniform).
- Opacity index (0-100)
- Predicted opacity (higher = more opaque).
- Freeness (CSF ml)
- Estimated Canadian Standard Freeness affecting machine drainage.
- Fiber cost ($/ton)
- Estimated fiber raw material cost per ton of paper.
- Total input (%)
- Sum of all fiber percentages (auto-normalized to 100% for calculations).
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersSoftwood kraft (%) = 30, Hardwood kraft (%) = 40, Mechanical pulp (%) = 0, Recycled fiber (%) = 30 = 5 input(s) provided
- Calculate Tensile indexTensile index = sw * 95 + hw * 65 + mech * 40 + rec * 4568 = 68
- Calculate Tear indexTear index = sw * 100 + hw * 55 + mech * 45 + rec * 4064 = 64
- Calculate Burst indexBurst index = sw * 90 + hw * 70 + mech * 35 + rec * 4267.6 = 67.6
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What happens if my four fiber percentages don't add up to 100%?
The calculator normalizes whatever percentages you enter so they sum to 100% before computing any blend properties, dividing 100 by your total percentage and scaling each fiber type by that factor. The Total input (%) output shows your raw, un-normalized sum so you can see whether normalization was applied, but every strength, formation, opacity, and cost index is calculated from the normalized values.
Why does adding mechanical pulp raise opacity but lower the strength indices?
Each fiber type carries fixed coefficients in the underlying weighted-average formulas: mechanical pulp has the highest opacity coefficient at 95 but the lowest tensile (40), tear (45), and burst (35) coefficients of the four fiber types. Since every index is a straight linear combination of your normalized fiber percentages against these coefficients, shifting furnish share toward mechanical pulp mechanically raises the opacity blend while pulling down every strength index in proportion.
Are the fiber cost figures based on current market pricing?
No — they use flat reference prices built into the calculator: $800/ton for softwood kraft, $700/ton for hardwood kraft, $400/ton for mechanical pulp, and $300/ton for recycled fiber, blended by your normalized percentages. These are rough approximations rather than live quotes, so substitute your own supplier pricing if you need an accurate cost comparison.
What does the freeness (CSF) output tell me, and how is it estimated?
Freeness estimates how quickly the furnish blend will drain on the paper machine wire, in Canadian Standard Freeness milliliters — it's a weighted average of typical freeness values for each fiber type, from 650 for softwood kraft down to 100 for mechanical pulp, scaled by your normalized percentages. Higher freeness generally means faster drainage and a higher achievable machine speed, but since it's a linear blend of typical values rather than a measured furnish freeness test, use it to compare recipes directionally rather than to predict an exact drainage rate.
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