A functional device is defined by its specification, and most disputes about functional orthotics are disputes about a sheet of paper nobody wrote. Two suppliers can quote the same words and build different products, because the words describe an intention rather than a geometry.
The specification is the document that closes that gap. It is not a marketing asset and it is not a clinical record; it is the build instruction, and it should be complete enough that a different technician could produce the same pair from it.
This article describes the fields we require before starting a functional order, why each one exists, and what happens when one is left vague.
What functional means in production terms
Functional describes a device built to influence how load is distributed and how the foot is supported during movement. It is not a synonym for firm, and it is not a claim about an outcome. It is a description of the design intent.
In production, functional translates into a small number of variables: the geometry of the shell, the position and height of the posting, the depth of the heel cup, the stiffness of the material and the thickness distribution. Those five variables are what a specification has to pin down.
An accommodative device uses the same variables differently: more coverage, softer materials, less defined posting. Both are legitimate, and the specification should say which one is being built, because a technician who does not know will build something in between.
That is the first field on our form: purpose, in plain words. Support, alignment, load distribution or accommodation, with a sentence describing what the device is meant to do in the shoe the client will wear.
The purpose sentence is worth writing first and in the buyer’s own words. A sentence such as hold the heel and spread load across the middle of the foot is buildable; a sentence such as improve biomechanics is not, because it describes an ambition rather than a device.
The five geometry fields
Shell geometry describes the overall shape: how much arch fill, how the medial and lateral edges run, whether the device is full length or forefoot posted. A drawing or a reference pair is worth more than an adjective here.
Posting describes where and how much. Position matters more than amount in most conversations, and a specification that says only how much leaves the technician guessing where. We ask for position, height and whether the post is intrinsic or extrinsic.
Heel cup depth and stiffness decide how the device holds the calcaneus and how it feels in the shoe. A deep, firm cup is supportive and demanding; a shallow one is comfortable and less controlling. The specification should state the intent rather than the millimetre.
Material and thickness complete the geometry. Thickness interacts with shoe volume, so the shoe fields belong on the same sheet. A specification that names a material without a thickness is a specification that will be interpreted differently by two technicians.
It is worth describing the device in the language of the shoe rather than in the language of the clinic. A specification that says the device should hold the heel and fill the arch tells a technician what to build; a specification that says the device should address a particular movement pattern tells them what the clinician was thinking, which is useful context and not a build instruction. Both belong on the sheet, in separate fields, because a technician who confuses context with instruction will build the wrong pair and a clinician who confuses instruction with context will approve it. The separation is simple and it removes most of the ambiguity that produces remakes in this category.
Where a posting is specified, the direction matters as much as the amount. A specification that names a medial post without saying whether it is intrinsic or extrinsic leaves a decision that changes both the feel and the shoe fit. Writing both fields takes a moment and removes a conversation that otherwise happens after the pair has been built.
Materials, covers and the durability conversation
Functional devices usually need a firmer base than accommodative ones, and the material choice follows from the load profile rather than from preference. We build on TPU and EVA families among others, and the choice is made against activity, body mass band and expected hours of use.
Covers matter more than buyers expect. A functional device with a thin, low-friction cover behaves differently from one with a cushioned cover, and the difference is felt in the first minute. The cover also decides durability, because it is the layer that sees shear.
Ask how the cover is bonded and whether the bond is checked. Delamination is the most visible failure in this category and the most preventable, and a factory that can describe its bonding process is a factory that has dealt with the problem.
Ask also whether the cover is replaceable. A device whose cover can be renewed extends its useful life, which matters for clients who wear one pair daily and for practices that see the same clients over years.
Where the client has worn a previous device, a photograph of it is more informative than a description. Wear patterns, compressed areas and lifted edges describe what the last device did in use, which is information no measurement contains.
A useful check is to read the material and thickness fields aloud to someone who has not seen the file. If they can picture the device, the fields are complete; if they ask a question, the answer belongs on the sheet. This takes a minute and catches the gaps that a specialist reader fills in automatically without noticing.
The shoe fields that prevent remakes
Four shoe fields belong on the specification: type, size, whether the footbed is removable, and the available volume. Without them, the device may be right and still unusable, and the remake conversation becomes a discussion about the client rather than about the order.
Volume is the field most often missing. A functional device needs depth, and a shoe with a glued-in footbed and a shallow toe box may not have it. A photograph of the inside of the shoe, with the footbed removed if possible, answers the question in seconds.
The shoe also determines the length of the device. A full-length device in a shoe that flexes at the ball will fight the shoe; a shorter device may be the better answer even when the clinical intent suggested full length. That is a design decision informed by the shoe, and it belongs before production.
Distributors building a range should define these fields per product line, so that clinics ordering from a catalogue answer the same questions every time. Consistency in the form is worth more than variety in the catalogue.
Where the client has no previous device, the shoe fields carry more weight. A first device built for a shoe with limited volume will often be judged by how it feels in the first hour, and that judgement is made with the shoe on, not with the device in hand. Asking the client to bring the shoe, trying the device in it before the appointment ends, and noting any pressure at the top of the toes takes ten minutes and prevents the most common first-device complaint.
Where a specification has to serve several shoe types for one client, write the primary shoe first and note the others as secondary. A device built for the primary shoe will often work in the others; a device built for a compromise between three shoes usually works in none of them, and the compromise is invisible on the sheet unless the priority is stated.
Review, sign-off and the moment before production
The review is the cheapest quality gate in the process. Before production, the specification should be read against the file and the shoe, and any conflict should be resolved in writing rather than on the bench.
In practice the conflicts are predictable: a posting that the shoe volume cannot accommodate, a device length that does not match the client’s activity, a material that is out of stock in the required thickness. Each is a five-minute conversation before production and a week-long problem after.
Sign-off should be explicit. We ask for written approval of the specification, referenced by order number, because a verbal approval is remembered differently by each side. That reference is also what makes a reorder a reorder rather than a new project.
Where the buyer is a clinic, the sign-off is usually the clinician’s. Where the buyer is a distributor, it is usually a technical contact who has seen the file. Either way, the signature belongs to a named person rather than to a job title.
The sign-off should include the shoe, not only the device. A specification approved without the shoe is a specification with an assumption inside it, and assumptions are what remakes are made of.
The approval step is worth protecting even in a small practice. When the person who designs also builds and also ships, the approval becomes a nod, and a nod is not a record. A single line in the order system that cannot be completed without a name is enough to keep the step real.
Remakes, reasons and the records that make them cheap
A remake policy is only workable when the specification exists, because it is the document that decides whether the device matches the order. Without it, every remake is an argument about intention.
Our position is that a remake attributable to our production is our cost, and a remake caused by a specification we received in error is a conversation with a proposed solution. Both outcomes depend on being able to compare the device with the approved sheet.
Log the reasons by field rather than by complaint. A pattern across ten remakes usually points at one field on the form, and changing the form is cheaper than changing the process. Two quarters of logging typically removes the largest single cause.
Keep the records together: file, specification, shoe information, production record. One order number, one folder. That habit is what makes the second year of a supply relationship easier than the first.
Remake conversations go better when the specification is on the table. The first question in any such conversation should be what the sheet said, and the second should be what the device does, and the third should be what the client experiences. Three questions, in that order, separate a production error from a specification error from a fit problem, and each of the three has a different answer. Most disputes in this category skip the first two questions and begin with the third, which is why they take so long and end so rarely to anyone’s satisfaction.
A specification sheet you can hand to a clinic
For distributors, the specification becomes a form that clinics fill in. It should be short enough to be completed during a consultation and structured so that the fields map directly onto the build instructions.
Eight fields are enough for most functional work: purpose, device length, shell description, posting position and height, heel cup intent, material and thickness, shoe fields, and the intended activity. Everything else is commentary.
Test the form on three real cases before printing it. If a technician can build from it without calling the clinic, the form works. If every case produces a phone call, the form is missing a field, and the phone call is telling you which one.
The form is not bureaucracy. It is the difference between a custom device and a device that happened to be made for one person, and that difference is what a clinic is paying for when it orders a functional pair.
It is worth keeping a small library of approved specifications, anonymised, as reference for new staff. Three or four examples teach a clinic more about what a complete sheet looks like than any guidance document.
Frequently asked questions
What is a functional orthotic?
A device built to influence load distribution and support during movement, defined by its shell geometry, posting, heel cup, material and thickness. Functional is a description of design intent, not a claim about an outcome.
What do you need to build a functional pair?
A measurement or a specification, the five geometry fields, the material and thickness, the shoe information and a plain description of purpose. Eight fields cover most functional orders.
Do you need the shoe as well as the foot record?
Yes. Volume, removable footbed and internal length decide whether the device can be worn. A photograph of the inside of the shoe is usually enough.
What is the minimum order?
Two hundred pairs for insoles, mixed across styles and sizes. Samples leave within three days of confirmation so the specification can be checked against a physical pair.
What happens if the device does not match the specification?
That is a remake attributable to our production and it is our cost. We compare the device with the approved sheet, and we log the reason by field so the form improves.
Can the top cover be replaced later?
In most constructions yes, and it is worth specifying. A replaceable cover extends the useful life of a device at a fraction of the cost of a new pair.
What certification applies?
European Union certification and ISO quality system certification. That is the full scope of the documentation we hold, and the documents are sent on request.
What we would do next
If you are writing a functional specification, send us the eight fields and we will confirm whether the design can be built in the shoe you describe. The insole categories page shows the ranges we build, the core technology page explains how the measurement feeds the design, and the FAQ page states minimums and transit in writing.
For related reading, see functional and accommodative orthotics and where biomechanics enters the process.
This article is intended for professional and educational reference. It is not medical advice. Foot assessment equipment produces measurements and images; clinical interpretation and any decision about care remain the responsibility of a qualified professional. Certification scope is limited to the documentation we hold: European Union certification and ISO quality system certification.