A buyer comparing packaging options usually compares two prices: pence for a carton, pounds for a box. That comparison is not wrong, it is just incomplete. A carton running an internal parts loop carries three further costs that never appear on a purchase order, and in most plants those three together are larger than the carton itself.
The invoice price is one number out of four
The four are the carton, the labour to make it up and close it, the damage it fails to prevent, and the cost of getting rid of it. Only the first is a line on a PO. The second is sitting in someone’s hourly rate. The third shows up as a rejection at goods-in, usually booked against quality rather than packaging. The fourth is a skip hire line in facilities. A returnable turnover box removes the first and the fourth outright, cuts the second to a fold-and-stack action, and changes the third rather than eliminating it.
Make-up and close-out are not free
A carton has to be folded, taped at the base, filled, taped at the top and labelled. On a bench packing fifty parts an hour that is a minute of the operator’s time that a rigid box does not need, because a rigid box is already up and closes with a lid or a stack. Multiply by shifts and by stations and it is headcount-adjacent, which is why it stays invisible: nobody posts a job requisition for carton folding.
Damage is booked against the wrong budget
A crushed corner at goods-in gets written up as a supplier quality issue or a carrier claim, not as a packaging decision made six weeks earlier. Cartons have almost no resistance to a point load on a corner; a strap pulled tight, a pallet overhang, a box hung up on a rack upright and the corner goes. If the part inside is machined or painted, the whole carton is now scrap. The comparison to run is not the price of the carton but the price of the carton plus the write-off rate it produces.
Disposal is a real invoice
Every carton that comes into a plant leaves it as waste. That means a baler or a compactor, a skip, a collection, and someone wheeling the skip. It is cheap per kilogram and constant every week, which is exactly the profile of a cost that never gets challenged. It also scales with volume, so it grows with the business in a way a box fleet does not.
Doing the arithmetic on one loop
Take one internal loop: machined housings moving from a supplier site to an assembly plant, four hundred movements a week. Cartons at 0.90 each is 360 a week. Add half an operator across the packing and unpacking stations, add a write-off rate of three parts a week at 40 each, add a weekly skip collection. A box fleet covering the same loop is a one-off purchase spread over the number of trips the box survives – and a PP corrugated box in an internal loop routinely survives hundreds. The crossover is usually inside a year, sometimes well inside it, which is the same conclusion reached in the carton bill you stop paying when you own the packaging.
Where the carton still wins
Three places. Any movement that leaves the site and never comes back, because there is no loop to amortise against. Any product where the carton is the retail unit. And any loop that runs for a few weeks a year – a seasonal line cannot pay back a fleet. We will say so if that is your situation; a fleet sold into the wrong loop is a fleet that gets abandoned in a yard.
What the comparison leaves out on the other side
The four numbers above are the carton’s costs. A returnable fleet has costs of its own and they should be in the same table rather than omitted. There is the capital, spread over the fleet’s life. There is washing, where the process requires it. There is repair and the labour that goes with it. And there is the administrative cost of running a loop: someone has to own empties, count them, and chase them. None of these are large individually and all of them are real.
The one that surprises people is the loop administration, because it is the only cost in the comparison that is a continuing commitment rather than a price. A carton requires nothing from anybody beyond being ordered. A box fleet requires a named owner for the empties and a count. Plants that skip that step end up with a fleet that works beautifully for two months and then runs short, at which point the cartons come back and the business case is quietly written off. Build the ownership into the plan before the first box arrives, not after the first shortage.
What we can do
We make returnable PP corrugated turnover boxes sized to the part rather than to a catalogue. Send us the movement – what moves, how far, how many times a week – and we will put the four numbers next to your carton spend, including the ones that are not on the PO.