E-Flute vs B-Flute: Which Board for Your Mailer Box

What is a flute in corrugated board?

Corrugated board is a sandwich. Two flat paper liners sit either side of a wavy middle layer, and that wavy layer is the flute. The size of the waves sets how thick the board is and how it behaves.

E-flute has small, tight waves packed close together, giving a board 1.5 mm thick. B-flute has taller, wider waves and comes out at 3 mm. Both are single wall boards, with one fluted layer between the liners.

You can see the difference by looking at a cut edge. E-flute shows a fine row of tiny arches. B-flute shows larger arches you can pick out one by one.

The flute also runs in one direction across the sheet. We set it so the waves run the right way for each panel, which helps the lid stay flat and the creases fold cleanly.

How do the two boards compare side by side?

The table sets out the main differences buyers ask us about. Neither board is better in every case; each suits a different kind of order.

Which board prints better?

E-flute gives the cleaner print. The small flutes sit close under the liner, so the surface stays flat and ink lands evenly. Fine text, thin lines and photographs hold their detail.

On B-flute the larger waves can show through as faint stripes, sometimes called washboarding. You notice it most on solid blocks of dark colour across a wide lid. Bold logos, simple patterns and one colour designs hide it well.

If you plan full colour on the inside as well as the outside, E-flute is usually the safer choice. Our guide to printing inside the lid explains how both faces are set up.

Which board protects fragile goods?

B-flute has more air in its waves, so it gives more cushioning between the product and anything that knocks the box. The walls also flex less over a long panel, which helps larger boxes keep their shape in a sack.

For glass jars, candles in vessels, ceramics and anything with a corner that can chip, B-flute is the usual starting point. Pair it with an insert that stops the item moving, because movement inside the box causes more damage than the knock itself.

Thicker board does not replace good packing. A loose glass jar in B-flute can still knock against its own walls, while a snug jar in E-flute often arrives fine. Choose the board and the insert together.

Our fragile goods mailer boxes are built on B-flute with fitted inserts for exactly this reason.

Does board choice affect your postal band?

It can. Every layer of board adds its thickness to the outside size, and some panels on a mailer fold over twice. Going from 1.5 mm to 3 mm adds a little to each dimension.

On a box well inside the Small Parcel band, that makes no practical difference. On a slim mailer aimed at the Large Letter band, with its 25 mm depth limit, it can be the difference between fitting and not.

If you are near a band edge, tell us the band when you ask for a quote. The guide to mailer box sizes and Royal Mail bands shows how to work the outside size out.

When to choose E-flute

E-flute suits products that are not easily broken and brands that want a crisp, retail feel.

• Clothing, scarves, socks and soft accessories that only need a neat box.
• Cosmetics and skincare in their own cartons or tubes.
• Art prints, cards and stationery where a slim parcel matters.
• Jewellery and small gifts presented in a smaller box.
• Designs with fine type, photographs or detailed full colour pattern.
• Subscription boxes posted in the Large Letter band.

E-flute also folds into very sharp corners, which gives the closed box a clean, boxy look on a shelf or in a photo.

When should you choose B-flute instead?

Pick B-flute when the product needs more protection or the box is large. Candles, glass bottles, mugs, plant pots and heavier homeware all sit better in the thicker board.

Larger boxes in the Medium Parcel band also benefit. A long lid in thin board can bow when the box is stacked; B-flute holds the panel flatter.

Think too about how parcels are handled. Boxes travel in sacks and cages with other parcels pressing on them. Thicker walls resist being squeezed out of shape on a long route.

B-flute looks good in plain or one colour print. Our brown kraft mailer boxes are often ordered this way, with a dark ink logo on the natural board.

Does kraft or white-lined board change the choice?

Both flutes come with either a brown kraft liner or a white-lined face. The liner is about colour and print; the flute is about thickness and cushioning. You choose them separately.

White-lined E-flute is the usual pick for bright full colour, because it combines a white face with the smoothest surface. Brown kraft B-flute is the usual pick for a sturdy plain box with a printed logo.

White ink and white underprint work on kraft in either flute. On B-flute, keep white underprint areas simple, as the ripple shows more under a solid white block.

If you are unsure, ask for a plain sample in each liner. Holding the two boxes side by side shows the colour difference far better than a screen.

How to decide in five steps

Most customers settle the board question in a few minutes with these steps.

1. Ask whether the product can break, chip or dent. If yes, start with B-flute.
2. Check the postal band. If you need Large Letter, start with E-flute.
3. Look at the artwork. Fine detail or photographs point to E-flute.
4. Consider the box size. Long lids in the Medium Parcel band suit B-flute.
5. If the answers conflict, ask for a sample in each board and pack a real order.

Send your product and artwork details and we will recommend a board. You can also try a logo on the box on the Design Your Mailer Box page first.

Ordering in E-flute or B-flute

Tell us the inside size, the board you prefer and how the box will be printed. Boxes start from £0.25 a box, and you get a written quote within one working day.

If you cannot decide, say so on the request. We will suggest a board based on the product, the print and the band, and explain why in a line or two.

A free design proof follows before anything is printed. After you approve it, production takes 4 to 6 working days and free tracked UK mainland delivery takes 2 to 3 working days.

Both boards arrive flat in bundles. E-flute bundles are slimmer for the same count, which helps if storage space is tight. When you are ready, request a quote for your boxes.