BOM (Bill of Materials)

In discrete manufacturing a bill of materials is a comfortable thing: a chair takes one seat, four legs, twelve screws. Multiply by order quantity and you are done. A garment BOM looks superficially the same — one shirt takes fabric, thread, buttons, a label, a polybag — and the resemblance is a trap. Almost every line in a garment BOM varies along a dimension that a flat BOM cannot express.

Why a textile BOM is a matrix

Take a shirt produced in three colours and five sizes. The main fabric line is colour-dependent: navy shirts consume navy fabric, white shirts consume white. The fabric *quantity* is size-dependent: an XS consumes meaningfully less than an XXL. The sewing thread is colour-matched to the shell. The buttons may be colour-matched or may not. The care label is identical across every variant. The size label is size-dependent and colour-independent. The polybag may change with size.

So the BOM is a grid of style x colour x size, in which some lines vary along both axes, some along one, and some along neither. Represented as a flat list, this style needs fifteen separate BOMs, which then have to be maintained in fifteen places every time the buyer changes a button. Represented properly, it is one BOM whose lines each declare which dimensions they vary along.

This matrix structure is the single clearest reason a garment factory outgrows a generic ERP. Generic systems model a BOM as parent item plus child items plus fixed quantities. To express a size-dependent fabric consumption they force you to create a separate item code and a separate BOM per size and colour combination, and the item master explodes.

Fabric is consumed as a rate, not a count

The second structural difference is the unit. You do not consume "one fabric" per shirt. You consume a length or a weight, and that figure comes from a marker — the cutting layout that arranges the pattern pieces on the fabric width to minimise waste. Marker efficiency is what determines consumption, and it depends on the fabric width, the size ratio being cut, and whether the fabric has a nap or a directional print that prevents pieces being rotated.

On top of the marker consumption sits a wastage allowance: end bits, cutting loss, shrinkage after washing, and rejected panels. The BOM figure is therefore net consumption multiplied by a wastage factor, typically a few percent for a plain fabric and materially more for a print that has to be pattern-matched. The exact allowance is a per-mill, per-fabric judgement, and it is one of the most consequential numbers in the whole system: it flows straight into [MRP](/glossary/mrp) as a purchase quantity and straight into costing as a material cost.

Set it too low and you are short of fabric mid-cut, which on an imported dye lot means a shade break or a delayed shipment. Set it too high and every quotation carries invisible padding and you lose orders you should have won. Mills that track actual versus BOM consumption per order can tune the allowance from evidence; mills that do not are guessing forever with the same number.

Trims, MOQs and the tyranny of small orders

Trims are cheap and they are where BOM discipline collapses. A shirt might carry twelve buttons, one main label, one care label, one size label, one hangtag, one polybag, thread and interlining. Each is a fraction of the garment cost, and each has a minimum order quantity from its supplier that has nothing to do with your order size.

A woven label supplier may not run below several thousand pieces. A custom button may have a mould charge. So a 500-piece sample order can require you to buy 5,000 labels, and the leftover 4,500 sit in the trim store forever, because they carry the buyer's brand and cannot be used on anything else. This is why trim MOQs belong in the BOM as planning parameters, not as a footnote in a purchase requisition — the true material cost of a short run is not the twelve buttons, it is the MOQ you had to absorb to get them.

The BOM is also the costing document

A BOM's second job is to price the garment. Extended across the order it produces the material cost, which under an [FOB model](/glossary/cmt-fob) is the majority of the sell price. A one percent error in fabric consumption on a large order is real money, and it is invisible: the shirts get made, the fabric gets used, and the shortfall shows up only in a gross margin that came in lower than the quotation promised, with no obvious culprit.

This is also why BOM version control matters more in apparel than almost anywhere else. Buyers change trims late. A button substituted at pre-production, a label revised for a new season, a fabric requalified after a wash test — each is a BOM revision, and each changes the cost. If costing runs against the current BOM but production consumed the previous one, the variance analysis is meaningless. Every BOM should be versioned, effective-dated, and locked to the order it was quoted against.

What a textile-aware BOM has to support

A BOM structure fit for apparel and textiles needs, at minimum: colour and size dimensions on any line that varies; consumption in length or weight with a per-line wastage percentage; alternate and substitute materials with their own consumption; supplier MOQ and order-multiple parameters; and versioning with an effective date, so that costing, [MRP](/glossary/mrp) and shop-floor issue all reference the same revision.

Vastra ERP models the BOM as a style-colour-size matrix rather than a flat parent-child list, holds fabric consumption per size with an explicit wastage allowance, and versions each revision against the order it was costed for, so [material planning](/features/supply-chain) and [product development](/features/product-lifecycle) work from the same document the quotation was built on.