What is an i6z file? The IUCLID PCN dossier, demystified

Sooner or later in poison centre notification work, someone sends you — or asks you for — “the i6z file”. If your background is regulatory affairs rather than IT, the term lands somewhere between a file format and a threat. It is neither: a .i6zfile is simply the packaged, submittable form of a PCN dossier, produced by ECHA’s IUCLID software or by tools compatible with it. This article explains what is actually inside one, how one gets built, and what you can — and should not — do with it.

What IUCLID is

IUCLID (International Uniform Chemical Information Database) is ECHA’s application for recording and exchanging structured chemical data. It predates poison centre notifications by many years — REACH registrations and biocides dossiers run on it too. When Annex VIII harmonised PCNs across the EU, ECHA implemented the PCN format as a set of IUCLID document types: your mixture, its components, its classification, its packaging each become a structured document with defined fields rather than paragraphs of prose.

Two IUCLID concepts explain almost everything else. A dataset is the live, editable collection of documents about your mixture. A dossier is a read-only snapshot of that dataset, frozen at a moment in time for submission. The .i6z file is the dossier, serialised to disk.

What a .i6z file actually contains

A .i6z is a compressed (zip-format) archive. Unpack one and you find:

• Data files — individual XML files (extension .i6d), one per IUCLID document: the legal entity, the mixture identification, the composition, each substance, the classification record, packaging, toxicological information, and so on.
• A manifest — manifest.xml, the table of contents listing every data file and attachment in the archive and how the documents link to each other.
• Attachments — binary files referenced from documents, most commonly the safety data sheet PDF.
• The dossier header— the “cover letter”: submission type (initial, update), market area, language, and flags such as limited submission or voluntary submission.

In other words, nothing exotic: structured data plus an index plus attachments, zipped. The value is not in the container but in the structure — every field sits where ECHA’s systems and the receiving member states expect to find it.

Three ways a .i6z gets built

You never write one by hand. It is generated by software, three flavours of which exist — matching the three PCN submission routes:

• IUCLID Cloud.ECHA’s hosted version, integrated with the Submission portal. You fill in the dataset in the browser and the dossier is created and submitted in place — many Cloud users never see the .i6z as a file at all.
• IUCLID 6 desktop. The installable application. You prepare the dataset locally, create the dossier, and export the .i6z to upload to the portal. This is the workflow where the file becomes a visible artefact you store, email and archive.
• Software via S2S.Compliance platforms build the same structure programmatically and push it straight to ECHA’s system-to-system gateway. Ufi Number works this way: the dossier is assembled from your product data in the current PCN format, and you can download the resulting .i6z for your records.

Why you never hand-edit one

It is technically possible to unzip a dossier, edit an XML file, and re-zip it. Do not. The documents cross-reference each other through identifiers recorded in the manifest; a hand edit that touches any of them produces an archive that may fail import, fail the validation rules, or — worst case — submit successfully with data inconsistent with what you think you notified. A dossier is also a snapshot by design: the honest fix for any error is to correct the dataset in the tool that owns it, create a fresh dossier, and submit that.

How to open one a consultant sends you

If a consultant or supplier hands you a .i6z and you want to see what is in it before it is submitted in your name, you have two honest options. The proper one: import it into IUCLID — a free IUCLID Cloud account is enough — and browse the documents in the interface, which renders every field with its label. The quick one: make a copy, rename it .zip, and open the archive to read the manifest and XML files directly; the field names are technical but legible, and the attached SDS is right there. Check at minimum the legal entity (is it yours?), the UFI, the market area in the header, and the composition — those are the fields where a misunderstanding with an external preparer is expensive.

Versioning: why an old .i6z can go stale

Every dossier is built against a specific version of the PCN format, which ECHA updates roughly annually alongside IUCLID releases — v8 has been current since April 2026. A submitted notification stays valid when the format moves on, but a fileprepared long ago and never submitted, or a dataset you want to update years later, may need migration to the current format before ECHA’s systems will take it. IUCLID handles most migration automatically on import; the practical rule is to regenerate dossiers from a current dataset rather than resubmitting archived files. The version history and what changes between versions are covered in PCN format versions.

What to remember

• A .i6z is a zipped snapshot of your notification: XML documents, a manifest, attachments.
• It is generated — by IUCLID Cloud, IUCLID 6 or S2S software — never hand-written, never hand-edited.
• You can inspect one safely by importing it into IUCLID or reading a renamed copy; you fix errors in the dataset, not the file.
• Archive submitted dossiers with their submission reports; regenerate rather than reuse old files when the format version has moved.