Home › Field notes › How to Write a Bag Specification Sheet That Production Can Build

Modular Bag Pro · 2026-10-10 · 2,755 words · 13 min read

A bag specification sheet has one job: to let a production team that has never spoken to you build the product without asking a single clarifying question. Most sheets fail that test because they describe the product a brand wants rather than the decisions a sewer has to make - they specify a fabric and a colour but not the stitch density, the reinforcement build-up or the tolerance on the attachment pitch. The practical cost of a thin sheet is measured in calendar: a complete specification compresses sampling to 6-10 working days, while a sheet with open fields pushes the same work into 12-15 working days of clarification and re-cutting. This guide sets out the six blocks a sheet needs, the field most sheets omit, and how to write acceptance criteria that settle an argument before it starts.

What a Specification Sheet Is Actually For

A specification sheet is a contract artefact, not a design document. A design document persuades; a specification sheet instructs. The distinction matters because the two audiences read it differently, and a sheet written to persuade leaves decisions open that the production floor then has to make by judgement.

Three groups will read the document. The pattern maker reads dimensions and tolerances. The purchasing function reads the bill of materials and the approved sources. The inspector reads the acceptance block and the defect classification. A sheet that serves one of those readers well and the other two badly will produce a correct sample followed by an inconsistent run.

The test for completeness is simple. Hand the sheet to someone outside the programme and ask them to list the questions they still have. If the list is longer than a few items, the sheet is not finished, and those questions will be asked later, when answering them costs material rather than time.

Volume changes the required precision. At MOQ 500 per configuration, a mis-specified tolerance is multiplied across a run rather than absorbed by a handful of units, which is why the same sheet that works for a prototype is inadequate for production. Precision is not bureaucracy; it is the difference between a deviation of one unit and a deviation of five hundred.

A useful discipline is to write the sheet as though it will be used in a dispute. Assume that in nine months somebody will need to establish what was agreed, and check that the document can establish it without a meeting. That single assumption removes most of the adjectives and most of the open fields at the same time.

Selection rule: Write the sheet so a stranger can establish what was agreed without a meeting, stripping adjectives and open fields at draft stage rather than when an enquiry at MOQ 500 forces the document into use.

Revision Header and Document Control

The header block is the least glamorous part of the sheet and the part that resolves the most disputes. It should carry five fields: document number, revision letter, date, the change made in this revision, and the name of whoever approved it.

The change field is the one usually omitted, and its absence is the reason two parties can hold different versions of a sheet and both believe they are right. "Rev C" tells nobody anything; "Rev C - webbing pitch corrected from 40 mm to 38 mm, anchor reinforcement extended one row" tells the inspector exactly what to look for on units built before and after the change.

Reference samples should be tied to the revision. Where a physical counter-sample exists, its number belongs in the header, so that the approved object and the approved document move together. A revision issued without updating the reference number produces a situation where the sample and the sheet disagree and neither is authoritative.

Distribution is the last piece. A revision that reaches the pattern maker but not the inspector is worse than no revision, because it creates a run where early units are inspected against one standard and late units against another. State who receives each issue, and keep the list short.

One further header field pays for itself: the superseded-revision disposition. State what happens to parts, patterns and material already bought against the previous revision. Without it, a change intended to improve one unit produces a shipment in which some units carry the old build and some the new, which is harder to explain to a retail buyer than the original defect.

Bill of Materials: The Fields That Matter

A bill of materials lists what goes into the product. Most lists name the item and the colour; the useful ones name the property that has to hold. The table below shows the difference on five common lines.

The third column is what makes a substitution controllable. If a fabric becomes unavailable, a sheet naming only "600D polyester" allows a substitute that meets the description and fails the product. A sheet naming the coating type and a hydrostatic head figure allows a substitute only if it performs.

Approved sources belong on the same line. Where a component has a single approved source, say so and give the part number; where alternatives are permitted, say which properties make an alternative acceptable. Silence on this point is read as permission, and permission given by silence is the most common origin of a mixed shipment.

Consumption figures belong on the same table. Stating the length of tape, the number of fittings and the metres of thread per unit lets a buyer check a quotation against the sheet instead of against a total. Where the two disagree, the disagreement is usually in wastage allowance, and having the consumption stated makes that conversation short rather than adversarial.

Verdict: State the property that must hold on every bill-of-materials line, including the 25 mm width tolerance on woven tape, because a list carrying item names and colours alone leaves wastage disputes unresolved until the cutting table.

Dimensions, Tolerances and the Callout Set

Dimensions without tolerances are not instructions. A stated width of 25 mm is compatible with anything from a loose 26 mm to a tight 24 mm, and on an attachment interface that spread is the difference between a pouch that mounts and one that does not.

The table below sets out the callout set for a modular chassis, with the tolerance band each line needs and the defect that appears when the callout is missing.

Note the last row, which is the field most sheets omit. Reinforcement extent is a dimension like any other, and stating it as "beyond the stitch line by a specified distance" converts a judgement call on the floor into a measurable line. Where it is missing, reinforcement is applied to whatever the operator considers sufficient, and tear-out returns appear later with no specification to point at.

Overall dimensions should be stated both empty and loaded where the product is soft. A soft module measured empty tells the buyer very little about whether it will fit in the intended cavity once filled.

Datums should also be stated. A dimension is only unambiguous if the point it is measured from is identified, and on a soft product the natural datum is usually a seam or a panel edge rather than an imaginary corner. Where two departments measure from different datums, both will report the product as conforming and one of them will be comparing against a figure the other never intended. Naming the datum on the drawing removes the ambiguity in one line and costs nothing to add.

Bottom line: Publish the 25 mm webbing width, the 38 mm vertical spacing and the 50 mm horizontal repeat as toleranced callouts with a named datum, since two parties reading one untoleranced figure will each report conformance and still disagree.

Construction Notes and Stitch Specification

Construction notes describe how parts are joined, and they are where most sheets go thin. Four lines carry most of the weight.

Stitch density, stated as stitches per unit length, governs seam strength and is the first thing a pattern maker looks for. Without it, seam strength varies with machine setting and operator, and the resulting spread is invisible until a loaded seam fails.

Seam type and seam allowance govern bulk and strength together. A bound seam and a turned seam of the same fabric behave differently at the anchor, and the difference shows up as tear-out rather than as appearance.

Back-tacking and stress-point reinforcement belong in the note block, not in a verbal instruction. Naming the positions where back-tacking is required converts a habit into a requirement and gives the inspector something to check.

Thread and needle selection closes the block. A thread ticket that is too heavy for the needle size causes skipped stitches and fabric damage at penetrations; a thread that is too light fails before the fabric does. Where a coated or laminated fabric is used, penetrations are also the path water takes, which is why seam strategy belongs in the same discussion as the hydrostatic head figure measured under AATCC 127.

Two further notes prevent recurring disputes. The first is edge finishing: whether raw edges are bound, turned or overlocked determines both bulk at the seam and how the edge behaves after washing, and it is rarely stated. The second is the position of labels and branding relative to reinforcement, because a label sewn across a load path becomes a failure origin rather than an identification feature.

Interface Definition for Modular Products

Modular products need one block that conventional bags do not: a definition of the interface that modules must satisfy. Five statements cover it, and all five should be written before the first module is designed.

The first is the geometry, restated from the callout table so the interface block is self-contained. The second is the mounting direction and the sequence of operations a user follows, because that sequence determines which retention features are needed. The third is the mass class per anchor row, stated as a figure rather than as an adjective. The fourth is the retention value that a mounted module must withstand, with the axis named. The fifth is what happens at the boundary: whether a module may straddle two rows, and whether the last row in a field is usable.

Compatibility with third-party accessories deserves its own line. If the product is intended to accept pouches the brand does not make, the sheet must state which geometry it conforms to, because "compatible" without a reference is not a specification and cannot be tested.

Finally, state the rule for future modules. A line saying that any module added to the range must satisfy this block without modification is the control that prevents interface drift across seasons. Without it, each new module quietly renegotiates the interface, and the family eventually stops working as a family. The geometry reference used across our range is documented under attachment grid engineering.

The block should also name what voids compatibility. Stating that a module exceeding the mass class, or mounted across two anchor rows without the stated reinforcement, falls outside the interface definition gives the inspector a rule to apply and gives the brand a defensible position if a return is traced to misuse rather than to the build.

Takeaway: Cover the interface in five written statements covering tape width at 25 mm, vertical spacing at 38 mm, horizontal repeat at 50 mm, stitch anchorage and maximum module mass, and let an inspector apply those statements directly.

Compliance, Testing and the Acceptance Block

The acceptance block is what the inspector reads, and it is where a sheet either prevents an argument or causes one. Three elements are required: the sampling plan, the defect classification, and the test methods with their limits.

Sampling follows ISO 2859-1, with an acceptance quality limit agreed in writing; AQL 2.5 is the conventional level for goods of this class. Stating the level is not enough - the defect classes have to be defined, because an inspection that treats a coating mark and a release failure as the same severity will produce a result nobody trusts.

Test methods should be named so a result can be reproduced. Fabric hydrostatic head is read under AATCC 127, tensile and tear behaviour under ASTM D5034, coating adhesion under ASTM D751, abrasion under ASTM D3884 or ISO 12947, care and dimensional stability under ISO 6330, and transit performance under ISTA 3A. A report quoting a value without naming the method cannot be compared with anything, including the next report.

Chemical and social compliance belong in the same block, listed as documents rather than as claims: REACH (EC 1907/2006) and EN 1811 for the European market, California Prop 65 and CPSIA for the United States, OEKO-TEX Standard 100 for textile inputs, and BSCI or an equivalent assessment for social compliance. Each is a document to be produced, not a property of the product.

Judgement: Build the acceptance block around a sampling plan citing ISO 2859-1 at general inspection level II with AQL 2.5 split into Critical 0, Major 2.5 and Minor 4.0, and issue that block before the 35-50 day production run begins.

Defects Commonly Found in Specification Sheets

Most sheets fail in the same handful of ways, and the patterns are worth checking for before issue.

The cost column is implied rather than stated above, and it is worth stating: every one of these defects is free to fix before sampling and expensive to fix after it. A sheet checked against this table takes under an hour to review and removes a category of rework that otherwise consumes the sampling window.

One further pattern deserves a line because it is invisible on the sheet itself: fields filled in by copying an earlier document. A specification inherited from a previous programme carries that programme's tolerances, fabric and hardware into a product with different loads, and the resulting mismatch is only discovered when the new product fails in a way the old one never did. Every inherited line should be re-derived rather than copied. A short column on the sheet recording why each tolerance was chosen achieves this: the reason survives, the number can be questioned, and a reviewer in a later season can tell the difference between a deliberate value and an inherited one.

Where a programme is unsure whether its sheet is complete, the fastest check is to send it for quotation and count the questions that come back. Each question is a missing field, and the pattern of questions is itself informative: repeated queries about the same block indicate that the block is unreadable rather than merely incomplete. Our production team returns that list as part of the quotation process, and the contact page is the route for a review before the sheet is issued.

Spec rule: Return a sheet that lacks the sampling plan, the datum or the 38 mm vertical spacing callout before quotation rather than after the T/T 30/70 deposit, because the same correction costs a meeting early and a shipment late.