Custom Gusset Bag Sizes Read From a Flat Sample
October 19, 2026A single sheet of A4 slid into a pouch that was cut to 210 millimetres will not go in. It catches on the weld at the corner, bows, and either tears or stops halfway. The pouch was made to the correct number and still fails, because the number on the drawing was an external dimension and what the sheet experiences is the internal one. Document pouch plastic is bought on external size and used on internal size, and the two differ by the weld on each edge and by the thickness of the film itself.
Once that gap is understood, the rest of the specification follows from it. Tolerance decides whether a pouch that fits one sheet fits a ream. Closure type decides whether the pouch survives being opened fifty times. Static decides whether sheets come out flat or cling to the film and jam a feeder. Clarity decides whether a document can be read without being removed.
None of these is difficult. What causes trouble is that they are usually specified one at a time, in response to a problem that has already appeared, rather than together at the point of ordering.
Internal Size Is the Only Size That Matters
An external measurement includes the seal. Every pouch has a weld running around it, and that weld is film that a sheet cannot occupy. A pouch quoted at 220 by 310 millimetres externally may give an internal space of 210 by 300 or less, depending on how wide the seal is and how many layers the film has.
The practical rule is to specify internal dimensions and to say the word internal. A supplier reading an internal figure will add the seal allowance and quote the external cut, and both parties then know what is being discussed. A supplier reading a bare figure has to guess whether the weld is included, and the guess is usually the one that makes the pouch cheaper to make rather than the one that makes it usable.
There is a second contributor that is smaller but real. Film thickness takes space on every axis. On a thin single layer pouch this is a fraction of a millimetre and nobody cares. On a laminated pouch with several layers and a stiff feel, the cumulative effect across four edges is enough to turn a comfortable fit into a tight one, and it shows up first on the corner where two welds meet.
A4 and A3 Internal Dimensions for Document Pouch Plastic
The A series is built on a fixed ratio, so the two sizes that matter here are 210 by 297 millimetres for A4 and 297 by 420 millimetres for A3. Those are sheet dimensions, not pouch dimensions. A pouch has to be larger on both axes by enough clearance that a sheet enters without being forced.
How much clearance depends on what goes in with the sheet. A single sheet slid in flat needs very little, a few millimetres on each axis. A folded document, a bundle, or sheets that have been stapled or clipped need considerably more, because the bulk is now three-dimensional and the pouch has to accept the thickest point rather than the flat one. Buyers who specify to the sheet and then load bundles end up with pouches that fit the first document and strain on the fifth.
The other case worth naming is the punched sheet. Documents destined for a ring binder carry holes that reduce the usable width, and a pouch sized tightly to the sheet edge will cover or crush them. Where the document has to remain binder-ready, the internal dimension has to be measured from the outer edge of the punched margin rather than from the sheet edge.
Tolerance Is What Separates a Fitting Pouch From a Tight One
A nominal internal size without a tolerance is not a specification. Cutting film to a fixed dimension is a physical process with variation in it, and the variation is larger on a soft material than on paper, because the film moves under the blade and relaxes afterwards. A pouch that is nominally correct can be produced a couple of millimetres under and still be within a normal tolerance.
That matters because the failure mode is asymmetric. A pouch made slightly large is mildly annoying. A pouch made slightly small does not close, or closes with the sheet buckled inside it, and the whole batch is unusable for its intended purpose. A sensible specification therefore states the minimum acceptable internal dimension rather than the target, and treats the target as a centre.
Tolerance also has to be stated on the seal width, for a reason that is easy to miss. A pouch whose internal space is correct but whose seal wanders will have one corner where the weld intrudes further than the others, and that corner is where sheets catch. Consistency of the weld matters more than its width.
Closure Types and What Each One Costs in Daily Use
The closure is chosen on how often the pouch is opened, not on how secure it looks. A press-to-close zip profile is cheap, lies flat, and is fine for a document that is filed and left. It wears, and after repeated opening the two sides of the profile stop engaging cleanly, which shows up as a pouch that appears closed and is not.
A slider closure costs more and solves that. The slider forces the profile together mechanically, so engagement does not depend on the user pressing evenly along the length, and it survives repeated cycles far better. For a pouch that is opened daily, a document pouch plastic order specified with a slider is usually the cheaper decision over the life of the pouch, whatever it does to the unit figure.
Adhesive flaps and hook-and-loop tabs suit low frequency use, and a simple open mouth with no closure suits pouches that are sealed once and never reopened. Button and string ties appear mainly on archive and presentation work. None of these is wrong. Each is wrong when it is matched to the wrong opening frequency, and the failure appears weeks later rather than on delivery day.
Static Behaviour Decides Whether Sheets Feed or Cling
Static is the specification most often left out and the one that produces the strangest complaints. Some films generate and hold a surface charge readily. A sheet dropped into such a pouch clings to the wall, and when it is pulled out it drags, curls, or carries a second sheet with it. In an office this is an irritation. In a machine feeder it is a jam.
The remedy is either a different film or an additive that bleeds to the surface and dissipates charge. Additives are not permanent, and their effect declines over time and with heat, so a pouch that behaved well on delivery may behave differently after storage. Where documents will be scanned, printed or machine-fed, this is worth stating explicitly at the ordering stage rather than discovering later.
The interaction with print is worth noting as well. A charged surface attracts dust and holds it, which shows up as specks on a clear pouch and as pickup on any printed area nearby. Background on how static and other protective properties are treated in this category is covered in the anti-static and UV protection guide, and the ESD Association publishes its standards work at esda.org.
Clarity and Haze Are Two Different Specifications
Clarity and haze are routinely treated as one property and they are not. Clarity describes how sharply an object is seen through the film. Haze describes how much light is scattered as it passes through, which appears as a milky cast. A film can be low in haze and poor in clarity, or the reverse, and a document read through it will look acceptable in one case and soft in the other.
For a pouch whose job is to let a document be read without being removed, clarity is the specification to state. For a pouch whose job is to show that a document is present, or to protect it while obscuring the contents, translucency is acceptable and haze is irrelevant. Stating which one applies prevents a supplier from optimising the wrong property.
Gloss interacts with readability in a way that surprises buyers. A high gloss film reflects overhead light, and a document behind it can be harder to read than the same document behind a matt film with nominally worse optical properties. If the pouch will be read under office lighting, ask for a sample and read through it in the room where it will be used.
What to List When Ordering Document Pouch Plastic
Six items make the order answerable. Internal width and height, stated as internal and as a minimum. The sheet size and the condition the sheet is in, flat, folded, bound or punched. The closure type, with the expected opening frequency. Whether static behaviour matters, and what the document will be fed into. Whether the document must be read through the film. And the quantity.
Of these, the second and the fourth are the ones that cause the most rework. A pouch specified to hold A4 will hold A4 flat and nothing else, and a pouch specified without a static requirement will be made on whatever film is running that day. Both are avoidable with one extra line each.
How document and specialty films are handled in this market sits in the document and specialty packaging overview, and the plastic envelope comparison covers the case where a mailing function is also required.
Document pouch plastic is specified on the inside, at the minimum, and for a stated opening frequency. Do those three and the first batch is usable on arrival. Scheduling and freight questions belong with the sales team.
