Shipping a heavy item by parcel: box strength, void fill and when to use a crate

A heavy item usually survives the first knock. The box often does not. Once a side splits or the base sags, the item starts to move inside, and that is when a 30 kg parcel breaks itself and anything near it.

Most of what leaves our plant in Jaipur is dense for its size: cartons full of tape rolls, rolls of film, rolls of paper. So at our plant, a weak box worries us more than a fragile product does. The two problems need different answers.

Here is the short version. Use a double-wall box that is rated for the weight. Keep the item at least 6 cm away from every wall. Block it with material that holds its shape instead of loose fill. Seal every seam with wide tape. And check the carrier's per-parcel weight limit before you pack, not after. Once the packed weight goes past about 25 kg, a crate, or a pallet with a freight service, is often the safer choice.

The box numbers below come from the DHL Express essential packing guide (valid from 25 February 2026). It is the clearest public table I know that ties a box's strength to the weight inside it. Other carriers are quoted from their own pages, which I read in November 2026.

How strong does the box need to be?

It must be strong enough for the weight it carries, and that strength should be measured, not guessed. The DHL guide gives a table, and I would use it even if you never ship with DHL.

Two numbers matter here.

Bursting strength tells you whether the wall will tear open when something pushes on it. Edge crush tells you how much load the board carries standing on its edge, which is what stacking is.

A heavy item tests both.

Box makers do not all quote in the same units, so let us do the arithmetic. 1000 kPa is about 10.2 kg/cm², and 1200 kPa is about 12.2 kg/cm², which is how many Indian box makers state bursting strength. In the United States, boxes carry an ECT rating in lb per inch. 7 kN/m works out to about 40 lb/in and 8 kN/m to about 46 lb/in. A common 32 ECT single-wall box is only about 5.6 kN/m.

That is the gap that catches people out.

If I were buying boxes for a 25 kg product, these are the two numbers I would write on the purchase order. Paper GSM and the box maker's word are not enough.

In India we usually order boxes by ply. 3-ply is single wall, 5-ply is double wall and 7-ply is triple wall. Ply alone tells you very little, because two 5-ply boxes made from different papers can differ a lot in strength. Ask your box maker for the bursting strength and the edge crush of the finished board, in writing. The DHL guide also says to look for the manufacturer's stamp on the box, which states its construction and strength.

Three more rules from the same guide are worth keeping, and we would follow them for any carrier.

1. Do not reuse old boxes for heavy items. A used box has already lost some of its rigidity.
2. Choose the size carefully. An under-filled box collapses and an over-filled box bursts.
3. Leave at least 6 cm between the item and every wall and corner, and plan the box size around that gap.

Check the carrier's weight limit before you pack

Per-parcel limits decide the method, so look them up first.

1. Royal Mail. Its page on packaging and sending heavy items sets 20 kg as the most any single parcel can weigh, and asks you to split anything heavier into a second box. It recommends a double-corrugated box for heavy contents.
2. Parcelforce. Its conditions of carriage allow up to 30 kg per parcel, with up to 1.5 m in length and 3 m for length and girth combined on standard UK services.
3. India Post. The Speed Post Parcel (Domestic) page (updated 30 October 2026) allows a gross weight up to 35 kg, a length up to 1.5 m, and 3 m for length and girth combined.
4. UPS. Its heavy package guidance asks for a yellow heavy package sticker on anything over 70 lb (31.5 kg on its own page), and treats a package over 150 lb as freight.
5. DHL Express. Above 25 kg its guide moves from a box table to a "specialist packing method".

I would keep this list at the packing table, because the limit decides the box, the blocking and sometimes the carrier. For private couriers in India, ask your account manager for the per-piece limit and the heavy-parcel surcharge, and get both in writing.

They differ by service and by contract, so I would never assume the figure from one courier holds for another.

Why loose fill fails under a heavy item

This is the part I would think hardest about, and it is the part closest to what we make.

UPS says it plainly. Packing peanuts and crumpled paper will not protect a heavy shipment, because both crush and shift under the load. The DHL guide makes the same point in another way. Some void fill sinks or deflates under the weight of the contents, and the box ends up with empty space again.

Air pillows have the same limit. We make air cushion film, and I am happy to see it used to fill gaps around a heavy item. I would not let it carry the item's weight.

Honeycomb paper and bubble wrap are good at protecting surfaces from scuffs, but they are not a floor for 30 kg either.

A heavy item needs blocking. That means pieces that hold their shape under load and stop the item moving.

1. A base pad of folded or laminated corrugated board, at least 6 cm thick, under the item.
2. Corner posts or end caps made from corrugated board or dense foam, so the item's weight goes into the walls and corners of the box, not into one soft spot.
3. For machinery, wooden battens screwed to the base so the item cannot slide at all.
4. Then, and only then, light void fill in the small gaps that remain.

Our guide to choosing cushioning by product weight and fragility explains the difference between cushioning, void fill and blocking in more detail.

How to pack it, step by step

1. Take off or secure every part that can move: handles, lids, doors, wheels. Pack loose parts separately in a bag or small box.
2. Wrap the item against scuffs and scratches. This layer is for the surface, not for shock.
3. Put the base pad in the box. Centre the item on it with its heaviest end down.
4. Fit the end caps or corner posts so the item sits at least 6 cm from every wall.
5. Fill the small gaps that remain, press down on the top, and add a top pad before you close the box.
6. Seal with tape at least 48 mm wide, using the H method on both the top and the bottom. The DHL guide adds more strips for heavier shipments. A heavy box sealed with one strip down the middle is the classic failure.
7. Above 25 kg, add straps. DHL does not endorse strapping below 25 kg, because it can damage its machinery and the parcel. Above 25 kg it calls strapping an ideal way to strengthen the shipment, when applied correctly.
8. Put the label on the top face, flat and away from seams, and a spare copy inside the box. Add "This way up" arrows. DHL says it cannot guarantee the orientation of a parcel, but its teams do look for these marks.
9. Weigh the packed box and write the weight near the label.

Two checks you can do yourself

We suggest both before the first real shipment, not after the first complaint. Neither needs any equipment.

1. The lift check. Lift the packed box the way a handler would, by its two bottom edges, and hold it off the floor. If the base bulges or the sides bow outwards, the board is too weak or the base pad is too thin.
2. The tilt check. Tip the box slowly onto each of its four bottom edges in turn. If you feel the item shift, or hear it knock, the blocking is not tight enough. Fix it and tip it again.

When both pass, run a proper drop test on one sample. Our guide to running a drop test in your own warehouse shows how to do it fairly.

When should you switch to a crate or freight?

I would stop trying to make a cardboard box work when any one of these is true. Each one means the box is being asked to do a crate's job.

1. The packed weight is above the carrier's per-parcel limit, or above 25 kg on DHL Express.
2. One person cannot lift the packed box safely. Most parcel networks still lift by hand at some point.
3. The item has feet, castings or sharp corners that will punch through corrugated board. The DHL guide says sharp items need a protection case or a box-in-box, and should never be strapped to a pallet without secondary packing.
4. The item is tall and top-heavy, so it will tip if it is laid on its side.
5. The value is high and there is no second piece to send if this one breaks.

There are two main options, and we would choose between them by weight and by where the item is going.

The first is a crate. Plywood is the simplest for exports, because wood processed to be free of pests, such as plywood, falls outside ISPM 15, the international standard on wood packaging. A crate made of solid timber that crosses a border usually has to be treated and marked to that standard, so ask your crate maker for it.

The second is a pallet with a freight service. The item is bolted or strapped to a pallet, covered and shipped as part of a truck load. In India this is often booked as part-truck-load. It costs more than a parcel, but the item is moved by forklift instead of by hand, which suits a 60 kg machine much better than any box.

Where our materials fit

We make tape, air cushion film and paper cushioning. We do not make corrugated boxes or crates, so the box numbers in this article are DHL's, not ours.

That also means I should be honest about a heavy parcel. The box and the blocking do most of the work. Our part is the tape that holds the seams and the cushioning that protects the surface and fills what is left. Both matter, but neither can rescue a box that is too weak for its load. We would rather tell you that than sell you more fill.

If you have a heavy item and you are not sure whether it belongs in a box or a crate, send us its weight and its size through the contact page. We will tell you which tape and cushioning suit it, and if it needs a crate, we will say so.