Lingerie Tech Pack: What Factories Actually Need (And What You're Probably Missing)

Most founders submit a lingerie tech pack believing they've done everything right. The flat sketches are neat. The colourways are labelled. There's a page for trims. The factory confirms receipt and the process begins.

Three weeks later, the sample arrives. The underwire channel is too narrow. The wing has been constructed in a way nobody specified. The elastic tension is wrong and nobody can explain why, because nobody wrote it down.

Here's the thing: the problem is rarely the factory. The problem is that the document was designed to satisfy a brief rather than to communicate a standard. Those are different documents. Factories work from the second kind. Most founders send the first.

A lingerie tech pack is not a design document. It's a manufacturing instruction set. Every element either gives the factory enough information to make a decision correctly, or leaves a gap they'll fill using their own judgement. That judgement is based on their preferred method, their existing tooling, and their most recent order. Not yours.

This is where most lingerie and swimwear sampling failures begin: not on the production floor, but in the document sent before cutting starts.

What a Factory Does With Your Tech Pack

Understanding how a factory reads a tech pack changes how you write one.

When a new document arrives, a technical team assesses whether they can produce it based on what they're shown. They're looking for: clarity of construction, specificity of trims and components, viable measurements, and realistic production requirements. If the document is unclear, they don't email you for clarification before cutting. They make an assumption, note it, and proceed. If the document is incomplete, they default to their existing patterns and processes.

This isn't negligence. A factory producing for dozens of clients simultaneously cannot pause production to interpret vague specifications. Their job is to manufacture to a standard. Your job is to define that standard precisely enough that their interpretation matches your intention.

The most common factory response to an underspecified tech pack: the sample looks approximately right but feels commercially wrong. The silhouette is close. The construction is functional. But the details that define whether a garment is worth producing were decided without you.

The Sections Most Lingerie Tech Packs Get Wrong

Technical Drawings vs Flat Sketches

There's a persistent confusion between design flats and technical drawings, and it costs brands real money.

A design flat shows aesthetic intent: the proportion, the styling lines, the visual reference. A technical drawing shows construction intent: where seams fall, how components connect, what exists on the inside of the garment that's invisible from the outside.

A factory needs the technical drawing. The design flat is useful context. It is not a manufacturing instruction.

A technical drawing should show: seam lines and seam types, all components including internal ones like underwire channels, boning casings, foam cup layers, and modesty panels, stitch types on key seams, and all join points where different materials or panels connect. If a component isn't drawn, the factory will decide what to do with it. That decision may not match your expectation.

Construction Notes

Construction notes are where most lingerie tech packs are thinnest. "Sew elastic to top band" is not a construction note. It's an observation.

A useful construction note specifies: which type of elastic, what tension it should be applied at (stretched, relaxed, or a specific ratio), whether it's folded, turned, or applied single layer, what stitch type secures it, and whether the finish is visible on the outside of the garment.

The same principle applies to underwire channels, strap attachments, closure methods, lining construction, and any seam that involves a trim or component rather than fabric alone.

If a detail has more than one way of being done (and in lingerie, almost every detail does), the construction note needs to specify which method you require. "As per previous sample" is not a specification. It assumes a shared memory the factory may not have, or may not apply consistently.

Trim and Component Specification

A trim page that lists "ring and slider" and "fold-over elastic" has documented that trims exist. It hasn't specified them.

Every trim and component should be specified with: material composition, width or size, colour or colour code, finish, supplier or approved equivalent, and placement. For functional trims like underwires, boning, closures, and bra backs, you should also include the technical function the component must perform and the dimensional tolerance it must fall within.

Underwires specified only by width will be interpreted differently by every factory. Different underwire gauges behave differently under the breast. The difference between a 0.6mm and a 0.8mm wire is invisible in a spec sheet and significant in a fitting room. If you don't specify it, the factory uses what they have in stock.

Hook and eye closure width and row count should be explicit. A "standard three-row closure" on a 38E is not the same engineering decision as a "standard three-row closure" on a 32B. If the specification says the same thing for both, the factory has no reason to make that distinction.

Fabric Specification

Stating the fabric name or supplier reference is necessary but not sufficient. A fabric page in a lingerie tech pack should also include: composition percentage by fibre, weight in gsm, stretch percentage in width and length, recovery expectation, recommended care, and any finish or treatment (chlorine-resistant, UPF-rated, moisture-wicking) that affects processing.

For swimwear, chlorine resistance is not guaranteed by fibre composition alone. It's a function of the dyeing process and any applied finish. A fabric that looks identical to a chlorine-resistant fabric on a swatch card may behave entirely differently in water after six months. If your product makes a performance claim, the fabric specification needs to support it.

Where multiple fabrics are used in one garment (which in lingerie is almost always), each fabric should have its own specification row, and the placement of each should be clearly indicated on the technical drawing.

Colourway and Print Placement

"Dusty pink" is not a colour specification. It's a mood. A factory will match to their available dye lots and closest stock. The result may be the right family but the wrong value, wrong undertone, or incompatible with your other colourways when photographed together.

Colour should be specified with a Pantone reference (Pantone TPG for textiles, not Pantone Coated), a fabric swatch where possible, and an acceptable tolerance. If the fabric and the lace trim in the same style need to match, specify that requirement explicitly. Factories manage fabric and trims as separate sourcing streams. Matching them is not automatic.

For printed or embroidered fabrics, placement must be specified per panel, with dimensions from a fixed reference point. "Centre front" is not a placement instruction. "Centre of panel, 3cm from neckline seam" is.

Measurement Specifications and Fit Points

Measurements are the element most founders include and most factories find least useful in isolation. A measurement chart without a defined fit standard, a clear grade rule, and an agreed fit model is a list of numbers without a shared reference point.

A lingerie tech pack should specify: all garment measurements at the nominated grade (the size you're sampling in), the method of measurement (flat or stretched, before or after elastic application, specific tension if applicable), and the tolerance. Industry standard tolerance for lingerie is typically plus or minus 0.5cm on structural measurements and plus or minus 0.3cm on precision measurements like underwire placement, but your tolerance should be appropriate to your product.

For structured bras: apex position, underwire depth, underwire width, cup projection, and wing length are fit-critical measurements that must appear explicitly. A tech pack that specifies garment measurements but omits component placement measurements has not given the factory enough information to reproduce the fit.

What the Factory Needs Before the Tech Pack

There's a document that should exist before the tech pack: the development brief. It defines what the garment is trying to do, who it's for, and what standards it must meet before it's considered successful. The tech pack translates those decisions into manufacturing instructions. Without the development brief, the tech pack is a specification with no agreed purpose.

A factory can make it. They just can't assess whether what they've made is correct.

Most factories don't ask for a development brief. Most clients don't know to send one. The absence of it means approval decisions are made on subjective response rather than against a defined standard. "I'm not sure about the cup shape" is harder to resolve than "the cup is not meeting the agreed projection depth of 8.5cm." The first is an opinion. The second is a measurable specification the factory can actually address.

Before You Send the Next Tech Pack

Work through these before submitting:

Is every internal construction detail drawn as well as every external one? Is every trim and component named, sized, specified, and placed? Are colour references Pantone-coded rather than described? Are construction notes method-specific rather than observational? Are measurements accompanied by measurement method and tolerance? Is there a clear seam allowance specification per seam type? Does the document tell a factory what success looks like, not just what the garment looks like?

If any of these can't be answered yes, the document isn't ready. Sending it anyway passes the cost of incompleteness to the sample round. And sample rounds are expensive, slow, and rarely the last one.

The Real Cost of an Incomplete Spec

A revision round in lingerie typically costs between £800 and £2,500 depending on complexity and shipping. A three-round sampling process that should have been two rounds because the specification was unclear costs more than money. It costs four to eight weeks of development time, factory relationship capital, and (if the launch window narrows) the commercial opportunity the product was built for.

The spec document is not the exciting part of product development. It is, however, the part that determines whether the product that arrives matches the product you intended to create. Factories are skilled manufacturers. They are not mind readers. The more precisely you communicate, the closer the first sample will be to your standard, and the fewer revision rounds you'll need to get there.

A well-written lingerie tech pack isn't evidence of thoroughness. It's a commercial decision.

Sarah Denise Studio works with lingerie and swimwear brands on tech pack development, manufacturing specification, and sampling oversight. If your documentation needs a professional review before it goes to factory, book a consultation call and we'll go through it together.