Guide · Kraft paper
How to specifysack kraft paper.
Sack kraft is the strong, porous paper used in multiwall sacks for cement, flour, sugar and chemicals. A precise specification is what makes a sack survive filling, stacking and transport. These are the parameters that matter.
The key parameters
What each value tells you.
| Parameter | What it measures | Why it matters |
|---|---|---|
| Grammage (g/m²) | Weight of paper per square metre | Sack strength and the number of plies needed |
| Tensile strength (kN/m) | Force the paper withstands before breaking, in both directions | Resistance to tearing during filling and handling |
| Stretch (%) | How far the paper extends before breaking | Extensible grades absorb drops and shocks |
| TEA (J/m²) | Tensile energy absorption: strength and stretch combined | The best single indicator of drop resistance |
| Air permeance or porosity (Gurley, s) | How quickly air passes through the sheet | Fast filling of powders without bursting |
| Cobb (g/m²) | Water absorption of the surface | Resistance to moisture and print quality |
| Brightness | Whiteness of bleached grades | Print appearance for retail sacks |
The main types
Natural, white, standard or extensible.
| Type | Typical feature | Typical uses |
|---|---|---|
| Natural (unbleached) sack kraft | Brown, highest strength for its weight | Cement, building materials, minerals |
| White (bleached) sack kraft | Bright surface for printing | Flour, sugar, food and retail sacks |
| Extensible sack kraft | Higher stretch and TEA | Heavy and fast-filled sacks, fewer plies |
| High porosity grades | Faster air release | High-speed filling of fine powders |
Our grades
The nine grades we work with.
| Code | Grade | Weight | TEA index | Strength | Plies | Typical uses |
|---|---|---|---|---|---|---|
| SKE HP | Extensible, high porosity (unbleached) | 70 to 110 g/m² | 3.1 to 3.3 J/g | ●●●○ | 2 to 3 | Cement and dry mixes in valve sacks on high speed lines, low dust |
| SKE | Extensible (unbleached) | 60 to 100 g/m² | 3.3 to 3.4 J/g | ●●●○ | 2 to 3 | Cement and dry mixes; extra perforation possible |
| SKS HP | Semi-extensible, high porosity (unbleached) | 60 to 110 g/m² | 2.8 to 3.0 J/g | ●●○○ | 3 to 4 | Cement and dry mixes in valve sacks, no perforation needed |
| SKS | Semi-extensible (unbleached) | 60 to 100 g/m² | 2.7 to 3.2 J/g | ●●○○ | 3 to 4 | Dry mixes, cement, retail, e-commerce, animal products, charcoal |
| SKI | Standard improved (unbleached) | 60 to 120 g/m² | 2.9 to 3.2 J/g | ●○○○ | 1 to 4 | E-commerce, retail, delivery, animal products, charcoal, seeds |
| WSKS | Bleached semi-extensible | 60 to 100 g/m² | 2.7 to 3.2 J/g | ●●○○ | 3 to 4 | Dry mixes, cement, agriculture, food products |
| WSKS HP | Bleached semi-extensible, high porosity | 60 to 100 g/m² | 2.8 to 3.0 J/g | ●●○○ | 3 to 4 | Dry mixes, cement, agriculture, food products |
| WSKI | Bleached standard improved | 60 to 100 g/m² | 2.9 to 3.2 J/g | ●●○○ | 1 to 4 | E-commerce, retail, delivery, animal products, charcoal, seeds |
| KS | Kraft liner board for flat layers | On request | Not applicable | ●●●● | Single board | Corrugated board production and as a packaging material |
Your checklist
What to put inyour specification.
- 01Type: natural or white, standard or extensible
- 02Grammage and tolerance
- 03Tensile strength and stretch in both directions, or TEA
- 04Air permeance (porosity) and Cobb
- 05Reel width, reel diameter and core size
- 06End use, sack construction and filling method
Please note
Typical parameters only.
This guide explains parameters commonly used in international trade, for orientation. It is not a specification, an offer or a statement of available goods. Every deal sets its own specification in the written contract.
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