A costing sheet comes back higher than expected, and the first instinct is to blame the factory's markup. Nine times out of ten, the real problem was sitting in the Bill of Materials weeks earlier — a lining that was never listed, a thread type left as "matching," a button quantity calculated for the wrong size run. The factory didn't invent a cost. It found one that was always there and nobody had written down.
A fabric list is not a Bill of Materials
It's an easy shortcut to make: main fabric, a lining if there is one, maybe the zipper — call it done, hand it over as the BOM. The problem is that a garment is built from far more components than the ones that show up in a moodboard, and every single one of them needs a quantity, a supplier and a price before a costing sheet means anything.
What a complete BOM actually lists
A Bill of Materials worth the name accounts for every component that ends up in or on the finished piece, each with an exact quantity per garment, a named supplier, and a confirmed unit price:
- Main fabric and lining, with exact consumption per size — not just per style
- Interlining and interfacing, wherever structure is added
- Trims: buttons, zippers, drawcords, eyelets, snaps — every hardware piece, by exact count
- Thread type and consumption, which changes with stitch count and seam type
- Labels: brand, care, size, and any compliance labeling required by the destination market
- Packaging components, when they're supplied by the brand rather than the factory
Leave one of these as "TBD" or "same as sample" and it doesn't disappear from the garment — it just disappears from the costing conversation, until someone notices the invoice doesn't match the quote.
Where the incomplete BOM actually costs
The gap rarely shows up while the BOM is being written — it shows up in bulk, when the factory has to source a trim that was never confirmed, at whatever price and lead time is available on short notice, instead of the one that was actually costed. Multiply that across every missing line item and a "surprising" invoice starts to look a lot less surprising.
This is exactly the same discipline the tech pack and spec sheet are built around one step later in the process — different document, same principle: nothing gets left to "the factory will figure it out." If you haven't already, that's the distinction covered in tech pack vs. spec sheet.
One more naming wrinkle worth settling before moving on: in Italian-speaking supply chains, this same document often goes by another name entirely. That's the subject of DIBA vs. BOM: are they the same document?
Not sure your BOM would survive a factory's first costing pass? Let's find out before bulk does.
Get in touch →