Corrugated board structure: how E, B, C, BE and BC flutes differ

A wave only a few millimeters high makes a large difference because it holds two flat sheets of paper apart. Corrugated board is built as a sandwich: linerboard on each face and a corrugating medium formed into a continuous wave between them. Holding the liners apart raises the moment of inertia of the structure, so the finished board is several times stronger than the same paper laid flat.

Each component has its own job. The liners take tension and compression, and the outer liner doubles as the printing surface for your logo and product information. Each wave of the medium works like a small support column between the liners, while the air channels between the waves cushion the contents against shocks in transport.

Flute height therefore has a direct effect on strength. A taller flute moves the liners further apart, so in many cases it adds more strength than a higher grammage.

B flute and C flute

B and C flutes are only 1 mm apart in height, and purchasing teams often overlook the difference. In practice they guard against different risks:

• B flute protects the surface. It has more flutes per foot, which gives it a tighter face that resists punctures from sharp objects. That makes it a good match for products that are rigid on their own, such as cans and bottles. Products like these carry much of the stacking load themselves, so what the box mainly has to resist is puncture.
• C flute protects the stack. Its taller, wider-spaced flutes handle stacking loads better. It is the standard specification for parcel boxes and consumer goods cartons that are loaded, unloaded and restacked several times on the way to the customer.

Combined flutes BE and BC

Bonding two flute layers together gives a 5-ply board. The two combinations serve different purposes:

• BE puts the print face first. Its outer face is B flute, smooth enough for good printing. The combined board is only 4 mm thick, the same as a single C flute, so it also folds cleanly. It suits branded goods that are too heavy for a 3-ply box and need a good print face.
• BC puts strength first. At 7.0 mm it is the thickest board we produce, with the highest resistance to vertical compression and impact of the five flutes.

2-ply board wraps products to protect them from scuffing and cushions them inside the box. It is not used to make the box body itself. We supply it in rolls, with a minimum order of 40 kg and a standard width of 48 in.

The weight bands for 3-ply and 5-ply are a starting point. The final specification also depends on how much of the load the product carries itself, how the boxes are stacked, how long they stay in the warehouse and how humid the storage area is.

Loads that will stand stacked in a warehouse for months, or cross borders in containers, are usually specified on BC flute. Raising the grammage of a C flute board is the weaker alternative. A heavier paper leaves the liners the same distance apart, while moving from 3-ply to 5-ply widens that distance directly and gives a clearer gain in strength.

Each flute also needs suitable liner and medium grades. For that side of the specification, see Corrugated paper grades: what they are and how to choose the right one.

Corrugated board also protects loads on the pallet, separates items inside the box and holds products on display in the store:

• Pads. Sheets cut to size and laid on pallets spread the weight of the product and reduce denting when loads are stacked.
• Partitions and dividers. They hold items in place so they cannot knock against each other, which greatly reduces damage to fragile goods such as glass bottles and electronic devices.
• In-store displays. Some brands build product stands from corrugated board. It is strong enough to hold the products and lighter than other display materials.

For more on pads, partitions and other sheet products, see Corrugated sheets. Boxes formed with inserts are covered under Custom corrugated boxes.

Start with three questions. How must the box look when it arrives? How high will it be stacked, and for how long? What is the packed weight of each box?

The answers usually point to one of these:

• E flute where appearance matters and stacks stay low
• B or C flute for general goods shipped within Thailand
• BC flute for high stacks, long storage, export and heavy loads. In these cases it is often better value than a lighter flute, once you count the cost of boxes collapsing in transit.

To decide between C and BC, look at all of these together:

• how much of the load the product carries itself
• whether boxes are stacked corner to corner in columns or interlocked
• how many layers high they go
• how long they stay stacked
• the humidity of the storage area
• the weight of each packed box

Use figures from your own operation for every factor in the list. Weight per box alone does not settle the choice. All the sheet specifications we produce are listed on Corrugated sheets.

If your own customers ask where the packaging paper comes from, our plant is certified to ISO 9001 and FSC and can trace the paper sources to back up your answer.

Frequently asked questions

Should I choose B flute or C flute?
Let the main risk decide: puncture points to B flute, stacking points to C flute. For a rigid product where the danger is a sharp object piercing the box, the denser face of B flute, with more flutes per foot, is the better guard. For boxes that will spend time stacked in a warehouse or on pallets, the taller profile of C flute holds up better under vertical compression.

Is the difference between 3-ply and 5-ply only thickness?
5-ply is also stronger and holds up noticeably longer in high stacks. As a starting point, a 3-ply box suits packed contents of roughly 10–20 kg and a 5-ply box roughly 20–50 kg. The final specification depends on the stacking method, the number of layers, storage time, humidity and product weight together.

Which flute gives the best print quality?
E flute prints best. Its flutes are the shortest and most closely spaced of the five, which leaves a smooth outer face where the flute lines barely show. When the box also has to be strong, BE is the most balanced choice: its outer face is B flute, which still prints well, and the second flute layer adds strength.

Which flutes can your production line make?
E, B, C, BE and BC. For the finest print quality, our team recommends E flute.

Can I order sheets instead of formed boxes?
Yes. We produce sheets to the size you specify, for customers who form boxes on their own lines or who use the sheets as pads and dividers inside their packaging.