KA vs KI paper: how the two liner grades differ and which to choose

In the paper we use, KA and KI liners have the same burst strength. The differences that matter to a buyer are moisture resistance, color, print sharpness and the grammages each grade comes in.

KA holds up better on routes with humidity, long storage or sea freight. KI has a softer, more natural look and suits consumer brands whose boxes move through controlled conditions.

Reading KA and KI on a board specification

Look at the first entry of the board specification. That is the outer liner, and it is where KA and KI appear: KA150/CA105/CA105 or KI150/CA105/CA105, with everything after it identical. On a quotation the two options can look almost the same, KA150 against KI150.

A swap between the two touches the liner only. Box dimensions stay the same, and an existing die-cut design can still be used.

Outer and inner liners are specified separately, so one order can use KA on the outside and KI on the inside. Buyers usually pick the outer liner for the conditions the box travels through and the inner liner for how much the product rubs against it. When you place the order, name the grade and grammage of both liners. A request for a "strong box" leaves too much open. The board specifications we produce are listed under Corrugated sheets.

KA and KI compared side by side

For the full ranking of all five liner grades and their grammages, see Corrugated paper grades: what they are and how to choose the right one.

KA has a distinct golden-yellow surface and KI is light brown. Liner color comes from the production process and the type of pulp, and it says nothing about recycled content. Reading the lighter KI as a liner with more recycled fiber is a common mistake.

KA is available in 125, 150, 185 and 230 gsm. KI stops at 185 gsm, so a job that needs the heaviest liner of the two has to use KA. For more on KA grammages and how to read a full board specification, see What is KA paper: grammages, specifications and typical uses.

What a switch to KI does to box strength

In dry conditions, a KI box performs like a KA box of the same construction. Burst strength measures the force needed to rupture a sheet of paper. In the paper we use, KA and KI are level on this measure and both rank second only to KH, with the full order running KH > KA = KI > WS > KK. Buyers who compare burst figures alone often conclude the two grades are interchangeable. That holds in dry conditions and stops holding in damp storage, as the moisture section below explains.

How much a box can take depends on grammage, flute type and the number of plies together, and each part has its own job. The liner takes impacts and punctures from outside. Stacking strength, also called compression strength, comes mainly from the flute and the number of plies, with the liner grade contributing little. Keep the flute and plies as they are, change the liner from KA to KI, and puncture resistance stays where it was. No flute change is needed. Corrugated board structure: how E, B, C, BE and BC flutes differ explains how flute and plies carry the load.

The risk in the switch is damp storage. KI is less moisture resistant than KA, so a KI box can lose strength sooner in a humid warehouse. Check where the boxes will be stored before making the change.

Moisture resistance is the main difference

Humid storage is where KA and KI boxes start to behave differently. Moisture resistance among the grades we produce runs KH > KA > WS > KI > KK, which puts KA in second place and KI two places lower, behind WS.

The first sign usually shows in the bottom layer of a stack. Boxes that left the factory within specification begin to buckle after a period in a damp warehouse. Board loses strength as it takes up moisture, and the bottom boxes go first because they carry the weight of everything above them and sit closest to the floor, where the air is most humid.

In many cases, three storage changes fix a moisture problem better than upgrading the liner, and they add nothing to the paper cost:

• Stack boxes on pallets or floor boards, off the concrete floor
• Leave space from the walls for airflow
• Keep stacks within the designed height

When the liner itself has to change, choose it by condition:

• Long transit or long storage: KA
• Moisture as the main risk, as in cold rooms and frozen food: KH, which has moisture-resistant additives mixed into the pulp

Print quality and appearance

For print sharpness, the order is WS > KH > KA > KI > KK > CA. KA sits one place above KI, even though KI is the lighter-colored liner.

KI offers a softer tone. Printed colors look gentler on its paler base, which suits brands with a natural image.

When sharpness and an exact shade matter most, specify WS, a white-top liner. It gives the sharpest print and the closest Pantone match of any grade we produce.

Choosing between KA and KI

Two details settle the choice faster than anything else: how the boxes are stored and how far they travel.

• Choose KA if the boxes will face humidity, sit in a warehouse without temperature control, go by sea or stay in storage through the rainy season.
• KI is a good fit when conditions are controlled all the way and the printed box is what shoppers see.

If your boxes fit neither case clearly, think about whose hands they reach first. A box that goes to a warehouse team is judged on strength and moisture resistance, and color matters little. A box opened by the end customer is judged partly on how it looks.

How the two grades compare on price

KA and KI cost about the same, so changing from KA to KI is an unreliable way to save money. The grade name is only one part of a job price, which also depends on grammage, flute, the number of plies and quantity, as shown on the quotation for that job.

KK sits at a lower price level. It is the cost-saving grade, made from recycled fiber, and it ranks last of all for both strength and moisture resistance. On boxes that spend a long time stacked or travel long distances, the saving tends to disappear, because damaged goods often push the total cost higher.

Frequently asked questions

Are KA and KI equally strong?
Yes, for burst strength. In the paper we use, the two liners match on burst strength and both rank second only to KH, so in dry conditions they perform alike. They differ in moisture resistance and color.

Does switching from KA to KI require a flute change?
The existing flute can stay. Check storage conditions first, since KI is less moisture resistant than KA.

Which grade suits e-commerce?
Storage time decides it. For fast-moving stock kept in controlled storage, KI gives parcels a natural look that supports the brand. For stock held for long periods, or parcels shipped to areas where humidity is uncontrolled, KA is the safer choice.

Is KI available in 230 gsm?
KI comes in 125, 150 and 185 gsm only, while KA goes up to 230 gsm. If the job needs the heaviest liner, choose KA.

Can one order use KA outside and KI inside?
Yes. Outer and inner liners are specified separately. The outer liner is usually chosen for the environment and the inner liner for abrasion from the product.