Home › Field notes › Modular First Aid Module Specification: Capacity Tiers, Internal Reten

Modular Bag Pro · 2026-10-11 · 3,457 words · 16 min read

A modular first aid module is specified by four things: a capacity tier given as a volume band and a dimensional envelope, an internal retention method, a one-handed opening geometry, and an identification scheme that still works in poor light. Every reference begins at 500 units, prototypes take 6-10 working days, a production run takes 35-50 days, goods are released against AQL 2.5 and numbers are quoted FOB Xiamen. This page addresses bag organisation only. It is not medical advice and it does not define clinical content; what a module holds is decided by the organisation carrying it, under its own rules and any local requirement that applies.

What a First Aid Module Specification Actually Fixes

A specification for a first aid module fixes the container and leaves the contents to someone else. That boundary is not modesty; it is the only defensible position for a bag maker. What belongs inside a module depends on the organisation, the activity, the distance from definitive care, the training level of the people carrying it and the rules that apply where they operate, and none of those are things a bag specification can know.

What a specification can and must fix is the geometry. How much volume the module offers, what envelope it occupies on the host panel, how the items inside are kept from migrating, how the closure behaves under a gloved hand, and how the module announces itself when the light is bad. Those five decisions determine whether the module works, and all five are engineering questions.

This page addresses bag organisation only. It is not medical advice and it does not define clinical content. No statement here should be read as a recommendation about what a kit should contain, how much of anything it should contain, or what any item does. Those decisions belong to the responsible organisation and, where relevant, to the clinicians and regulators it answers to.

The practical consequence for a buyer is that a module is bought as an empty, graded, labelled container. The buyer fills it. That division makes the specification easier rather than harder, because the performance requirements can be stated without reference to the contents: a volume band, an envelope, a retention method, an opening force and travel figure, and a marking scheme.

The most common specification error is the reverse of this: a buyer asks for a module "suitable for X items" and receives a module whose internal dimensions happen to fit those items today and nothing else next season. Specifying the envelope and the retention instead produces a module that survives a change of contents, which is the point of calling it modular.

Spec rule: Write a first aid module specification as a volume band, a dimensional envelope, a retention method, an opening force and travel figure and a marking scheme, and never as a contents list, because a specification written around contents stops working the moment the contents change.

Capacity Tiers: Grading Volume Without Naming Contents

Capacity is graded by volume band and by envelope, not by what the module is intended to hold. Three tiers cover most civilian programmes, from a belt or chest-mounted module up to a full panel module worn on a backpack. The tier is chosen by how much a person is expected to manage at one time and by where the module physically sits, both of which are decisions the organisation makes.

Tier 1 is a small module sized to sit on a belt, a chest rig or the shoulder strap of a host pack. Tier 2 is the general-purpose size and the one most programmes standardise on, because it is large enough to be organised internally and small enough to be carried on a panel without dominating it. Tier 3 is a panel module intended to live on a backpack frame or in a lid compartment and to be opened on the ground rather than in the hand.

Volume is stated as a measured figure rather than a nominal one, and the measurement method is stated with it. A litre figure obtained by filling a module with a graduated medium and a figure obtained by multiplying external dimensions disagree by a wide margin on a soft module, and the disagreement is the reason two suppliers can quote different capacities for what looks like the same pouch.

The envelope matters more than the volume in practice. A module that holds enough but is 20 mm too deep for the panel it is meant to sit on will not close, will not sit flat, and will catch on everything it passes. The envelope is dimensioned against the host panel before the volume is finalised, which occasionally means accepting a slightly lower volume to get a usable shape.

Verdict: Grade modules by measured volume band plus a dimensioned envelope checked against the host panel, and standardise a programme on Tier 2 at 1.0-2.5 litres, because that band is large enough to organise internally and small enough not to dominate the panel it rides on.

Internal Retention Compared: Elastic Loops, Slip Pockets and Moulded Dividers

Retention is what separates a module from a bag with a zip. Its job is to keep each item in a known position through a season of being carried, dropped and opened, so a person reaches for position rather than searching a space. Three methods cover nearly all modules, and each has a distinct failure.

Elastic loops hold cylindrical and near-cylindrical items at a defined width. They are cheap, light and forgiving of small dimensional changes, which is why they dominate. Their failure is that elastic relaxes: a loop sized to grip a 25 mm item at the start of a season will grip a smaller item less firmly two years later, and a loop that has been stretched over an oversized item once will never return to its original tension.

Slip pockets hold flat items and are the only sensible method for anything card-shaped. Their failure is depth and contrast: a pocket deep enough to retain is deep enough to hide, and a dark pocket in a dark cavity hides its contents completely. A pocket with a cut-away front or a contrast binding solves the visibility problem without giving up retention.

Moulded or stiffened dividers create fixed zones and are the best method where the module is opened on a surface and the contents are counted rather than grabbed. Their failure is weight and inflexibility: a divider set adds mass and fixes the internal layout permanently, which is the opposite of what modularity is supposed to buy.

Retention width is specified, not implied. A loop strip is dimensioned as a set of widths against the items it will hold, stated in millimetres, and the tolerance is written down, because "elastic loops" on a drawing tells a production line nothing it can inspect. The same applies to pocket depth and divider spacing.

The retention material also has to survive cleaning. Elastic that has been repeatedly wetted with a cleaning agent loses recovery faster than elastic that has not, and a loop that no longer grips is a retention failure rather than a cosmetic one. Where the cleaning regime is aggressive, a woven tape with a defined stretch or a moulded retainer outlasts bare elastic.

Takeaway: Specify retention as a dimensioned set of loop widths, pocket depths and divider spacings in millimetres, choose elastic only where the cleaning regime is mild, and avoid moulded dividers on any module whose contents will change between seasons.

One-Handed Opening: Pull Geometry, Slider Travel and Grip

One-handed opening is a geometry problem and it is specified in numbers or it does not happen. Three figures govern it: how far the slider has to travel to clear the contents, how much force the opening needs, and how large the gripping feature is. A module that fails any one of the three needs two hands, whatever the marketing says.

Slider travel is the distance from closed to the point where the contents can be reached. A module that opens around two sides has roughly twice the travel of one that opens on a single face, and while the two-sided version exposes more, it needs either a stable surface or a second hand to hold the other side. For a module intended to be opened in the hand, a single-face opening with a short travel is the correct geometry, and the opening is sized so the contents are visible as soon as it is clear.

Opening force is specified as a range rather than a maximum. Too little and the module opens when it is dragged through scrub or thrown into a vehicle; too much and it cannot be opened with a cold or gloved hand. The lower bound is the one most often forgotten, and a module that has opened itself in transit is worse than one that is slightly stiff.

The gripping feature is where glove compatibility is won or lost. A slider with a cord pull of 3 mm diameter is a bare-hand feature; a moulded grab handle or a webbing loop sized for a gloved thumb is a gloved-hand feature. The pull is attached so that it remains outside the closed module, because a pull that tucks inside has to be found before it can be used.

The closure itself carries a strength figure. Fabric for the module body is qualified for breaking strength by the grab method published as ASTM D5034, and any coated liner by the coated-fabric methods under ASTM D751; both are run on the finished cloth rather than on the raw roll, because bonding changes the result.

Selection rule: Specify a single-face opening with travel under 250 mm, an opening force range rather than a maximum, and a moulded grab pull projecting at least 15 mm, because a module that needs a surface or a second hand cannot be opened where it will actually be used.

Identification, Colour and Retroreflective Area on a Module

Identification does two jobs: it tells a person which module this is before it is opened, and it tells a second person where the module is in the dark. The first job is solved by colour and text, the second by retroreflective material, and neither is solved by a small embroidered cross in a tone close to the body colour.

Colour is chosen for contrast against the host rather than for appearance. A module that is visible on a black pack may disappear on a hi-visibility one, and a team running both is better served by a single module colour with a high-contrast border than by a module colour matched to each chassis. Where a colour carries a regulatory or customary meaning in the operator's jurisdiction, that meaning is confirmed with the organisation rather than assumed.

Text is specified by character height and contrast rather than by wording alone. A label that reads at 300 mm under office lighting may be unreadable at arm's length under a headlamp, and the failure is a legibility one. A light field with dark characters outperforms dark-on-light in most low-light conditions, and a label placed on the opening face is read before the module is opened rather than after.

Retroreflective material is specified as an area in square centimetres and a position, and it is placed on the outer face rather than on the harness side or the back panel. A narrow piping run of a few millimetres is a trim detail; a panel of defined area returns enough light to be identified at distance under a headlamp or vehicle beam. Where the module sits low on a pack, a second small panel on the top edge keeps it visible from above.

The mark itself should survive cleaning. A printed mark on a coated cloth that is wiped weekly will fade long before the module wears out, and a faded identification mark is a failure of a safety feature rather than of branding. Where the cleaning regime is aggressive, the mark is applied as a heat-transferred or sewn element instead of a surface print.

Bottom line: Specify module identification as a high-contrast body colour with a stated character height on the opening face plus a retroreflective panel whose area is stated in square centimetres on the outer face, and apply the mark by transfer or sewing where the module will be wiped weekly.

Matching the Module to the Host Bag: Envelope and Weight Placement

A module that works alone can still fail on the host. Two interactions decide it: whether the envelope fits the panel without fighting neighbouring modules, and where the mass ends up relative to the wearer's back. Both are checked in dimensions before anything is ordered.

Envelope fit is a grid question. A module occupying four columns of a standard grid consumes a defined width, and two modules side by side either share the grid cleanly or overlap the seam between them. The grid used across this range is built on 25 mm webbing at 38 mm vertical spacing with a 50 mm horizontal repeat, and a module envelope is dimensioned as a whole number of columns against that repeat rather than as a free dimension.

Depth is the dimension that causes the most trouble. A module that sits proud of the panel catches on doors, vegetation and vehicle edges, and a module that is too shallow cannot hold what it was sized for. The depth figure is set against the host panel and written into the drawing, not left to follow from the volume.

Weight placement follows from where the module sits. Mass carried high and close to the back is comfortable and stable; mass carried low and far from the back pulls the wearer backwards and increases the moment on the shoulders. A heavy module is therefore placed high and close, and a programme that puts its heavy module on the outside of a pack at hip height has made a load-carriage decision by accident.

The host matters as much as the module. A module sized for a chest rig behaves differently on that rig than on a backpack panel, because the chest rig is opened in front of the body and the pack panel is opened behind it. Small modules intended for body-worn use are usually developed alongside modular chest and waist platforms so the opening geometry is tested where it will actually be used.

Judgement: Dimension the module envelope in whole grid columns against the 50 mm repeat and place heavy modules high and close to the back, because depth that fights the panel snags in service and low, outward mass pulls the wearer backwards.

Sealing, Wipe-Down and Returning a Module to Service

A first aid module gets dirtier than any other module on a pack, and it is the one most often expected to be clean. Two features answer that: a lining that can be wiped and a way of telling whether the module has been opened since it was last checked.

The lining decision is a coating decision. A smooth coated lining wipes clean; an unfinished one holds contamination and moisture. Water resistance of the coated cloth is measured by the hydrostatic method in AATCC 127, and the resistance of the surface colour to a wiping action by AATCC 8; both are run on the finished, coated cloth and both have to be re-run if the coating supplier changes.

Seams inside the module are bound or sealed. A raw seam allowance inside a wiped cavity holds fluid, and fluid held in a seam is the reason a module smells and stiffens after a season. Binding a seam costs one operation and removes the problem.

The opened-since-check indicator is the cheapest reliability feature in the whole specification. A tag, a seal or a numbered tie that has to be broken to open the module tells the next person whether the contents are as they were left, without opening it. It costs a few cents and it is what turns a periodic inspection from a guess into a check.

Reset procedure belongs to the organisation, but the bag has to support it. A card sleeve inside the lid, a flat cavity that can be emptied completely, and a liner light enough in colour to show soiling all make the check faster, and a check that takes two minutes happens every shift while one that takes twenty happens rarely.

No part of this section describes clinical practice or sterilisation. It describes how the article is cleaned and how a checker can see whether it has been opened; what standard of cleanliness an organisation requires, and what it does with the contents, are matters for that organisation.

Programme Facts: Modules and the Production Base Behind Them

Vetted partner facilities provide 4,950 m² of SGS-verified floor, 149 machines and 7 lines staffed by 137 people, with monthly capacity close to 200,000 units, and module envelopes are cut against a fixed grid repeat rather than free-dimensioned. That is what lets a module built this season still fit a chassis bought two seasons ago.

Bag production experience goes back to 2004 on the founder's side, and the company has operated since 2014. A module programme follows the standard route: approval sample, counter-signed pre-production piece, bulk under batch records, release at AQL 2.5. Prototypes take 6-10 working days, or 12-15 where the internal fitment is complex, and bulk takes 35-50 days once the pre-production piece is signed.

A Module Specification Checklist Buyers Can Issue

The list below is written so that every line can be inspected. A line that cannot be measured on a finished module is a preference, and preferences have a way of becoming disputes.

• State the volume band and the measured method used to obtain it.
• Dimension the envelope in millimetres and in whole grid columns.
• Specify retention as loop widths, pocket depths and divider spacings in millimetres.
• Set opening travel in millimetres, an opening force range, and grab-pull projection.
• Fix body colour, label character height and contrast, and label placement on the opening face.
• State retroreflective panel area in square centimetres and its position on the outer face.
• Name the cleaning agent, then select coating, seam construction and hardware against it.
• Require an opened-since-check indicator and an internal card sleeve.

Commercial terms sit beside the engineering and do not alter it: settlement runs T/T 30/70, an order opens at 500 units per reference, and pricing quoted FOB Xiamen is indicative only. Dedicated tooling, where the internal fitment needs it, falls between USD 300 and USD 2,500, and a sample carries a USD 50-150 fee refunded against the order. Lead time by mode is 25-35 days sea, 5-8 days air and 3-5 days courier, and most programmes split the first order across air and sea. Small body-worn modules are developed with modular EDC platforms, bespoke layouts run through custom modular backpack programmes, and the current module range is shown on the products page.

The line most often left out is the opened-since-check indicator, and it is the one that costs least. Everything else on this list makes the module work; that one makes the programme auditable.