# Which cardboard box suits your shipment? *A box is nearly always ordered on three numbers: length, width and height. The fourth characteristic – the flute, the profile inside the wall that decides how much weight that box can carry at the bottom of a stack – rarely makes it into the request. Since 2007 we have been the go-to wholesaler for cardboard boxes, and what happens when that choice is left to chance usually only reaches us afterwards: a shipment arriving with a collapsed bottom layer, or a pallet that has sagged after a night in a cold warehouse. This article explains what sets E, B, C, BC and EB flute apart, what each one does to stacking strength and freight cost, and which flute belongs on which shipment.* ## What corrugated board actually is Corrugated board is not thick paper. It is a structure: two flat paper layers (the liners) with a fluted layer in between. That wavy middle layer works like a row of standing arches. As long as the flutes stand upright, the box carries load; once they buckle or absorb moisture, the strength is gone. We sell the same material by the roll as [corrugated cardboard](en/protective-and-filling-materials/corrugated-board) for wrapping products, and every folding box in our [cardboard boxes](en/cardboard-boxes) range is built on the same principle. ### The build-up: liner, flute, liner The outer layers determine how the box looks and how well it resists puncturing. Two paper types are used for this: kraftliner from virgin fibres, which is stronger and more moisture-resistant, and testliner from recycled paper, which is more economical and perfectly adequate for most shipping boxes. The middle layer – the flute itself – sets the thickness, the springiness and the load-bearing capacity. ### Why flute direction decides how much the box carries In an upright box the flutes run from top to bottom, like small columns. In that direction corrugated board is surprisingly strong. Lay the same box on its side and the load presses across the flutes – they fold flat at a fraction of the same weight. That is why a pallet with tipped boxes collapses far sooner than a pallet with boxes standing squarely. The same rule applies if you cut corrugated board to size yourself: run the flutes in the direction the pressure will come from. ## The flute types side by side Flutes are identified by a letter. The letter says nothing about quality and everything about flute height and the number of flutes per metre. A fine flute means many small arches: rigid, smooth and easy to print on. A coarse flute means fewer, taller arches: springier and better at absorbing impact. FluteThickness (approx.)Flutes per metreStrongest qualityTypical useF flute0.8 mmapprox. 600Very fine print qualitySmall consumer packagingE flute (micro flute)1 – 1.5 mmapprox. 300Smooth surface, minimal bulkLetterbox and product boxesB fluteapprox. 3 mmapprox. 160Rigid, good edge crushStandard shipping boxesC fluteapprox. 4 mmapprox. 140Balance of cushioning and rigidityLarger shipping boxesA fluteapprox. 5.5 mmapprox. 120High cushioning and stacking strengthLight, bulky, fragile goodsEB flute (double)4.5 – 5 mmcombinedStrong and printableRetail packaging that also shipsBC flute (double)approx. 7 mmcombinedHigh stacking and puncture strengthHeavy and valuable shipmentsTriple wallfrom approx. 10 mmcombinedMaximum strengthMachinery, parts, export### E flute: thin, smooth and space-saving E flute, also called micro flute, is at roughly 1 to 1.5 mm the thinnest flute you will meet in transport packaging. Because the flutes sit closely together, the surface is flat enough for sharp printing. The real gain is bulk: an E flute box takes up considerably less space than the same box in B flute, both on the packing bench and in the shipment itself. That matters most when a box has to fit through a letterbox slot, where every millimetre of wall thickness comes off your product. ### B flute: the workhorse of the shipping box At roughly 3 mm thick and 160 flutes per metre, B flute is rigid, prints well and performs strongly in edge crush – the property that counts the moment boxes are stacked. The vast majority of our [single wall cardboard boxes](en/cardboard-boxes/folding-boxes/single-wave-shipping-boxes) fall into this category. For parcels up to around ten kilos this is usually the logical choice. ### C flute: slightly taller, slightly more cushioning C flute is the taller sibling of B flute at around 4 mm. The flutes sit further apart, so the board flexes a little more and absorbs impact better. For larger boxes, where the wall panel is bigger and therefore more prone to bulging, that extra height helps. In practice B and C flute are often used interchangeably; the difference only shows up at large dimensions or with contents that can shift. ### A flute: plenty of air, plenty of cushioning At roughly 5.5 mm, A flute is the tallest single flute. All that air makes the board springy and surprisingly stackable, but also vulnerable: once an A flute is creased it does not recover. You mainly see it with light, bulky and fragile products. For ordinary shipping boxes B or C flute is the modern default. ### BC flute: the standard double wall Glue a B flute and a C flute together and you get BC flute: roughly 7 mm thick, built from two fluted layers and three flat ones. The rigid B flute takes the edge load, the taller C flute takes the knocks. That is exactly the combination you want for heavier shipments, and it is the construction used in our [double wall shipping boxes](en/cardboard-boxes/folding-boxes/cardboard-boxes-double-wave). ### EB flute: strong board with a presentable face EB flute combines a fine E flute on the outside with a B flute behind it, coming out at roughly 4.5 to 5 mm. You get micro flute printability with much of the strength of double wall. This combination is chosen when the packaging has to protect and look good at the same time – for instance with [printed cardboard boxes](en/printed-packaging-materials/printed-cardboard-boxes) that the customer unpacks personally. ### Triple wall: when the box has to be the crate With three fluted layers alternating with four flat ones, you arrive at board up to around 70% stronger than single or double wall. Our [triple wall shipping boxes](en/cardboard-boxes/folding-boxes/triple-wall-shipping-boxes) are meant for machine parts, tools, furniture components and sea freight – applications where a wooden crate would be the alternative. ### Why does the webshop list millimetres instead of a flute letter? Because thickness is what you actually work with. You will find single wall in 2 mm and 3 mm and double wall in 7 mm, which correspond to a fine flute, a B flute and a BC combination respectively. When comparing boxes from different suppliers, that millimetre figure is more useful than the letter: manufacturers apply small differences in flute height within the same letter. ## What flute type means for stacking strength “Strong” is not a single number where boxes are concerned. There are two kinds of strength that move independently, and most poor purchases come from confusing the two. ### Stacking load and puncture resistance are different things Stacking load is about vertical pressure: what holds up the bottom box on the pallet? That property sits in the edges, where the flutes stand as columns. Puncture resistance is about the wall: what happens when the corner of another pallet hits it? That property sits in the liners and in overall thickness. A fine, rigid flute scores well on stacking load but only moderately on puncture; a tall flute the other way round. Double wall is popular because it performs well on both. ### How much weight can a box carry? As a rule of thumb we work with single wall up to around 10 kg of contents and double wall up to around 40 kg. That is a guideline for what goes inside the box, not for what may go on top of it. When stacking, what really counts is how many layers go above, how long the stack stands and whether the weight rests on the edges or in the middle of the lid. ### So why does a double wall box at the bottom still collapse? For two reasons that have nothing to do with the flute. First, moisture: corrugated board takes up humidity, and at high humidity stacking strength can drop considerably within days. A pallet that spends a weekend in an unheated warehouse is no longer as strong as it was on packing day. Second, time: board creeps under sustained load. A stack that stands firm today may look different after three weeks. To prevent that, keep the load on the corners and secure the pallet tightly with [wrapping film](en/wrapping-film-shrink-film-top-sheets-pallets/stretch-film-wrap-film) or [strapping straps](en/strapping-materials/strapping-straps). ### What do pallet sheets do for stacking strength? An interlayer spreads the weight of the layer above across the whole layer below, instead of over a few chance contact points. [Cardboard pallet sheets](en/cardboard-boxes/cardboard-pallet-boards) in single wall do that job, keep the bottom boxes clean and stop strapping from cutting into the board. For the corners there are also [corner profiles](en/protective-and-filling-materials/corner-profiles), which spread the strap tension over a larger surface. ## What flute type means for your costs ### Thicker board costs twice: at purchase and at dispatch A double wall box costs more per unit than a single wall box of the same internal dimensions. It is also thicker, so the external dimensions are larger – and most carriers charge on volumetric weight. On a large box, four extra millimetres of wall per side make a measurable difference to the volume you are billed for. Reaching for double wall “to be safe” means paying for that reassurance on every single shipment. ### Is double wall always the safer choice? No. Double wall solves two problems: too much weight and too much external pressure. It does not solve the most common problem at all, which is a product moving around inside the box. A light product in an oversized double wall box arrives damaged sooner than the same product packed snugly in single wall with proper [filling material](en/protective-and-filling-materials/filling-materials) or [bubble wrap](en/protective-and-filling-materials/bubble-wrap-air-bubble-wrap). So choose the size first and the flute second. ### Where does a thinner flute genuinely save money? On light items shipped in high volumes. Moving from B flute to E flute for small articles saves on material, on storage space for the flat boxes and on shipping volume at the same time. For flat, light consignments you can drop the box altogether: [cardboard mailing envelopes](en/shipping-materials/cardboard-mailing-envelopes) and [air cushion envelopes](en/shipping-materials/air-cushion-envelopes) do the same job for less. ## Which flute for which shipment? Your shipmentRecommended fluteWhySmall and flat, through the letterboxE fluteStays within the maximum height and saves bulkWebshop orders up to approx. 10 kgSingle wall (B)Rigid enough, light and economicalLarger boxes, contents that shiftSingle wall (C)More cushioning across bigger wall panelsHeavy, valuable or stackedDouble wall (BC)High stacking load and puncture resistancePackaging the customer unpacksEB flutePrintable surface with transport strengthMachinery, parts, sea freightTriple wallOften replaces a wooden crate### E-commerce and small parcels For parcels that have to pass through a letterbox, height is the limiting factor and every millimetre of wall thickness comes off your product. For slightly larger parcels our [cardboard postal boxes](en/cardboard-boxes/order-postal-boxes-online) are the logical next step; for tubular items such as posters and drawings there are [shipping tubes](en/shipping-materials/shipping-tubes). ### Standard shipping boxes The [folding boxes](en/cardboard-boxes/folding-boxes) are the heart of the range and come in single, double and triple wall. They are delivered flat, which saves storage space, and can be closed in one movement with a [tape dispenser](en/tape/tape-dispensers). ### Moving and archiving With [moving boxes](en/cardboard-boxes/moving-boxes), something comes into play that rarely matters for shipping boxes: they are carried and stacked repeatedly. Hand holes in the side wall remove material at precisely the point where the stacking load sits, so for the bottom layer a box without hand holes is the better choice. The full range of [moving materials](en/moving-materials) is listed separately in the shop. ### On the pallet For pallet shipments the whole build-up counts: the [pallet](en/internal-transportation/wooden-pallets) itself, the boxes on it, the interlayers between them and the final wrap. Make sure boxes sit on the corners of the layer below rather than in the middle – that is where the strength is. ## Made to measure: your own size, creases and print Everything above concerns standard stock sizes. If you ship the same product again and again, there is a step that often pays off more than optimising within those standard sizes: having the box built around your product rather than the other way round. We supply [cardboard boxes](en/cardboard-boxes) in bespoke dimensions and shapes too, in single or double wall. ### Why internal dimensions lead on a custom box A box is always ordered on internal dimensions, never external. That sounds like a detail, but with double wall it adds up quickly: seven millimetres of wall thickness means well over a centimetre and a half of difference across both sides between what you measure and what will fit. So when requesting a custom box, give the dimensions of your product plus the clearance you want, rather than the external size of the box you use today. ### Creases: where the box folds, and why you can steer it Creases are the pressed fold lines in the board. They are applied across the flute direction, so the board bends cleanly there instead of breaking at random. The position of those lines sets the internal dimensions and therefore how your product sits inside. On a custom box that position is yours to choose, which opens up a few possibilities: - **Flaps that actually meet.** On a standard folding box the top flaps close against each other in the middle. If the ratio between length and width is off, they either fail to meet or overlap awkwardly – on a made-to-measure box that ratio is right. - **A self-locking base.** A box with a pre-glued crash-lock base opens in one movement and needs no tape underneath. At high volumes that saves noticeable time at the packing bench. - **Custom cut-outs.** Hand holes, ventilation holes or a tear strip are included in the same die. ### One extra crease cuts freight cost directly The most useful variant for webshops is a box with a second or third crease in the side wall. It lets you close the same box at a lower height when an order turns out smaller. You keep one item number in stock, use less [filling material](en/protective-and-filling-materials/filling-materials) and ship less air – and air is exactly what most carriers charge for through volumetric weight. If your order sizes vary, that single extra crease pays for itself faster than a heavier flute. ### Printing: which flute gives the best result? The finer the flute, the flatter the surface and the sharper the print. Photographic quality is achievable on E and F flute; on B flute the result is fine for logos and text, though the flute structure shows faintly across large solid areas. On C flute and double wall that ribbing is more visible – usually no objection on a shipping box. If you want a strong box that still looks considered, EB flute is the middle ground. Our [printed cardboard boxes](en/printed-packaging-materials/printed-cardboard-boxes) are supplied in one to four colours or full colour, on a brown or white surface. If you are looking for a cheaper route, [printed tape](en/printed-packaging-materials/printed-tape) or a [printed sticker](en/printed-packaging-materials/printed-stickers) on a plain box achieves a comparable recognition effect. ### From what quantity is a custom box worthwhile? That depends on the size: the larger the box, the higher the minimum order quantity. There is no fixed threshold, so it is worth simply asking. For printed boxes, allow roughly two weeks from approval of the digital proof. If you are unsure whether your annual volume justifies it, set the question against the other side of the sum: what do oversized standard boxes cost you per year in filling material and freight volume? ## Four mistakes we see most often ### Compensating for an oversized box with thicker board The most common error of all. Thicker board protects the box, not the contents. A product that can slide around inside will not be held still by double wall. Choose a size that leaves no more than two to four centimetres of play on each side, then fill the remainder. ### Ignoring flute direction when cutting board yourself If you cut dividers or protective sheets from board on the roll, the direction of the flutes decides whether the divider carries or sags. Run the flutes in the direction the load will come from. ### A single strip of tape on the seam The best box still opens if it is sealed badly. Use the H-method: one strip along the centre seam and one across each of the two end seams. For heavier boxes, [packaging tape](en/tape/packaging-tape) of sufficient width matters more than an extra millimetre of board; if you prefer an all-paper shipment, use [paper tape](en/sustainable-packaging-materials/paper-tape). ### Can I reuse a corrugated box? For most shipments, yes – but not at the bottom of a pallet. During the first use the flutes along the fold lines and edges are already crushed once, and those edges are exactly what carries the stack. Expect noticeably less stacking strength on a second round. So use reused boxes for individual parcels or the top layer, and put fresh boxes at the bottom. If a box has visibly bulged or been damp, it belongs with the waste paper: corrugated board is fully recyclable and comes back as testliner in new board. ## In short - **E flute** when bulk and a smooth, printable surface matter. - **B flute** for the bulk of shipping boxes up to around 10 kg. - **C flute** for larger boxes or contents that can shift. - **EB flute** when the packaging has to protect and present. - **BC flute** for heavy, valuable or stacked shipments up to around 40 kg. - **Triple wall** where a wooden crate would otherwise stand. - Always choose the **size** first and the flute second – a well-fitting single wall box beats an oversized double wall one. - Shipping the same product every time? Consider a **custom box**: your own internal dimensions, an extra crease for smaller orders and your own print if you want it. You will find every variant mentioned here in our [cardboard boxes](en/cardboard-boxes) range, along with the matching [protective materials](en/protective-and-filling-materials) and [shipping materials](en/shipping-materials). Ordered on working days before 3:30 PM? Then your order will be shipped the same day. Do you have questions about which size of [cardboard boxes](en/cardboard-boxes) is best suited to your situation? Please don't hesitate to contact us — by phone on [+31 184 – 614256](tel:+31%20184%20-%20614256), via [info@kortpack.nl](mailto:info@kortpack.nl) or via [WhatsApp](https://wa.me/31184614256). --- Published: 2026-09-10 12:10:00 Source: https://www.kortpack.nl