A bookcase arrives as a flat box and is assembled in a living room. The design follows from how freight is priced, since shipping an assembled item means paying to transport empty space.
Freight is priced by volume, not weight
A truck or container fills up long before it reaches its weight limit when carrying furniture.
Carriers price accordingly, using dimensional weight so that a bulky light shipment is charged for the space it occupies.
An assembled armchair is mostly air, and that air travels at the same cost per cubic foot as the material around it.
Flat packing multiplies what fits in a container
Disassembled components stack densely with minimal wasted space, so a shipping container can hold several times as many units.
The saving repeats at every stage, including the sea leg, the warehouse, the store's stockroom and the final delivery.
Warehouse storage is also charged by space, so denser packing lowers holding costs as well as transport costs.
Damage rates fall as well
Assembled furniture is fragile at its joints, and the greatest stress occurs during handling rather than during use.
Flat components in fitted packaging have no exposed joints, no protruding legs and no leverage points, so they survive handling better.
Fewer damaged deliveries means fewer replacements shipped, which is a substantial hidden saving in a low-margin category.
The design has to change to suit the method
Flat packing is not simply disassembly. Products are engineered around fasteners that a customer can operate with a single supplied tool.
Cam locks, dowels and threaded inserts exist because they align easily and tolerate imprecise assembly, and panel materials are chosen partly for how they hold those fasteners.
This is why flat-pack designs favour rectangular panels and right angles, since curved or solid components resist dense packing.
The last cost is transferred to the buyer
Assembly labour has not disappeared. It has been moved from a factory, where it would be paid for, to the customer, who performs it for nothing.
That transfer is a large part of the price difference between flat-pack and assembled furniture, alongside the freight saving.
Where customers decline the trade, retailers sell assembly as a service, which restores the labour cost as an explicit line rather than a hidden one.
The same logic now shapes what gets sold at all, since a design that cannot be packed flat carries a freight penalty on every unit for the life of the product.