What is KA paper: grammages, specifications and typical uses
When KA appears on a box specification, it refers to a kraft liner on the face of the corrugated board. KA is the liner grade used most in the Thai market, and it is the default because, among the papers we use, only KH has higher burst strength, and KA is easier to source and costs less than KH.
KA at a glance:
- Fiber: long fiber (kraft)
- Color: golden yellow
- Grammages: 125, 150, 185 and 230 gsm
- Position: outer or inner liner
- Moisture resistance: moderate
The color makes the grade easy to recognize. People on the production line and at goods receiving can tell a KA batch on sight, without checking the production order.
Where KA sits in the board
In corrugated board, a flat liner faces each side and a fluted medium runs between them. KA is a liner grade and can be used on either face. The medium is usually CA, a recycled-fiber grade that is not made to serve as a box surface.
When you compare boards, check burst strength before board thickness. The liner takes force first, from contents pressing outward and from knocks against the side of the box. KA handles that well because long fibers bond tightly, giving it higher tensile strength and better resistance to outside impact than short-fiber or recycled paper.
How to read a KA specification
Board specifications list the layers from the outer liner to the inner liner, separated by slashes:
outer liner (grammage) / medium / inner liner (grammage)
A common 3-ply example is KA150/CA105/CA105: a KA outer liner at 150 gsm, with CA 105 gsm for both the medium and the inner liner. The short form KA150/M means a KA150 liner with the standard CA medium, M standing for medium. 5-ply board follows the same pattern with more layers. KH150/CA125/CA125/CA125/KH150 is one example, used for cold-room work.
The specification is most useful when you compare quotations. Lined up side by side, two specifications show whether a price gap comes from the liner grade, the grammage or the number of plies. Look at the first and last grades closely, since the outer and inner liners take external force. The layers in between provide structure and keep cost under control.
Choosing a KA grammage
A higher grammage gives a tougher, denser sheet, and the weight and price of the board rise with it.
Box strength, measured by BCT (box compression test), comes from grammage, flute type and number of plies together. Change any one of them and the result changes, which is why a fixed chart matching product weight to grammage is unreliable. KA125 on C flute may carry more vertical load than KA185 on B flute.
If you want a thicker box, start with what the extra thickness should achieve:
- To stack higher in storage, moving from B flute to C flute is usually better value than adding grammage (see Corrugated board structure: how E, B, C, BE and BC flutes differ).
- For a better feel and appearance, a higher grammage or the WS grade fits better.
Where KA is used
KA suits boxes that travel and take knocks along the way: it absorbs handling impact well and is easy to source in every grammage. Industrial product boxes, machine parts packaging and most parcel boxes, which also carry load in transit, use it as their usual liner.
For general export, 5-ply KA board is common. It resists puncture and gives boxes the stacking strength they need inside a container.
KA or KH
KH is worth the extra cost when moisture is a major factor, since it is both stronger and more moisture resistant than KA. In other conditions KA is the more common choice: it is easier to source, costs less and has a shorter production lead time.
When another grade fits better
The time to change grade is at the quotation stage, before any damage happens. Two jobs are better served by a different liner.
| Job | Grade to use instead | Reason |
|---|---|---|
| Products sold on the look of the box, such as cosmetics and gifts | WS | The white surface reproduces Pantone shades most accurately; the golden-yellow base of KA shifts printed colors |
| Domestic distribution, single trip, tight budget | KK | Lower cost, and a single-use box does not need the extra strength |
Corrugated paper grades: what they are and how to choose the right one covers all five liner grades with their grammages.
Common misunderstandings about KA
- "KA is waterproof." KA resists moisture moderately, better than KI and KK, and it softens under sustained moisture. For those conditions, use KH or add a water-resistant coating.
- "KA must be the outer liner." KA works as an inner liner too. When the product rubs hard against the inner walls, KA on the inside can matter more than KA on the outside.
- "Switching from KK to KA makes the box stronger right away." A better liner improves burst and impact resistance. Boxes that crush when stacked need a change of flute or number of plies.
Flute and plies come next
Flute and the number of plies each change box strength more than a one-step move in grammage, so they deserve attention as soon as the liner is chosen. For the full range, Corrugated sheets lists every liner grade and grammage we produce, and Custom corrugated boxes shows the finished boxes we make.
Frequently asked questions
What is the difference between KA and KK?
KA is made from long fibers and has higher burst strength, while KK is made from recycled fiber and costs less. KA suits boxes stacked in storage for weeks or traveling long distances. KK is enough for single-trip domestic distribution.
Which grade is used for parcel boxes?
Mostly KA. Parcel boxes are handled many times and take knocks and load along the way, so an impact-resistant grade saves more in damaged goods than it adds in paper cost.
Which grade is used for export boxes?
It depends on the priority. For strength, use KA, usually as 5-ply board for general export. For sharp printing on the box face, use WS. KA and WS are the liner grades used most for export.
Is KA paper waterproof?
No. KA has moderate moisture resistance only. For long exposure to moisture or condensation, use KH, which has moisture-resistant additives in the pulp itself, or add a water-resistant coating. A coating adds its own cost and needs a coating plate made for each box size.
Should I choose KA150 or KA185?
The answer comes from a BCT calculation by our Technical Service team, since grammage alone cannot decide it. The calculation is based on how the product is packed and shipped, how high it is stacked and the weight of each box. On the same flute, a higher grammage sometimes adds less strength than it adds cost.
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Auto Boxes Technical Service Team
