What is a bill of materials (BOM)?
A bill of materials, almost always shortened to BOM, is the complete itemized list of everything needed to make one garment style. It records every fabric, lining, trim, label, thread, and packing item, along with quantities, specifications, colorways, and usually the supplier and cost for each line. If something physically goes into or onto the garment, it belongs on the BOM.
The BOM is the bridge between design and production. It turns a creative idea into a precise shopping and assembly list, so a factory knows exactly what to buy, in what quantity, from whom, and at what cost — with no guesswork left.
What a BOM contains
A typical apparel BOM breaks a style into every component, grouped by type. Each line carries enough detail to source and cost it without ambiguity.
- Shell fabric and lining, with composition, weight, and colorway.
- Trims: zippers, buttons, drawcords, elastic, interfacing.
- Labels: brand, care, size, and any compliance labeling.
- Thread and findings used in construction.
- Packaging: polybags, hangtags, cartons.
- Per-line quantity, supplier, and unit cost.
Where the BOM lives
The BOM is a core page inside the tech pack, the technical document that specifies how a garment is made. Sitting alongside the construction details, measurements, and graded specs, it gives sourcing and costing teams a single authoritative reference for every input the style consumes.
Why it controls cost
Raw materials and components account for roughly 60–70% of a garment's total cost. That makes the BOM the most cost-sensitive document in product development: a wrong quantity, a missed trim, or a pricier-than-planned fabric flows straight into margin. A clean BOM prevents production delays from missing materials and reduces the risk of over-ordering inventory that never gets used.
Why a bill of materials matters for fashion brands and ecommerce
For a small or growing brand, the BOM is where landed cost becomes real. It's the document that tells you whether a design is profitable at your target price before you commit to a single unit. Get it wrong and you discover the margin problem after the bulk run, when there's nothing left to adjust.
It also keeps a multi-style catalog coherent. As assortments grow, a structured BOM per style lets a brand reuse shared trims and fabrics across products, negotiate better on volume, and trace exactly which component caused a sourcing delay. It's unglamorous infrastructure, but it's what keeps cost and supply predictable as the line scales.
Practical takeaway
Build the BOM before approving samples, not after. The earlier the full component list and its costs are locked, the fewer surprises hit the bulk run — and the cleaner the handoff to sourcing, sampling, and quality control.