One of the most consequential decisions a publisher makes when moving to digital distribution is choosing between reflowable ePub3 and Fixed Layout ePub. Get it right and your content reads beautifully on every device. Get it wrong and you'll be paying to redo the work — or worse, shipping a product that frustrates readers.
This guide walks through the practical decision framework we use with clients at Daintra, based on converting thousands of titles across both formats.
What is Reflowable ePub3?
Reflowable ePub3 is the current gold standard for most eBook content. The text and layout adapt dynamically to the reading device — the same file displays beautifully on a phone, a tablet, an eReader, and a desktop app. Font size, line spacing, and margins are all reader-controlled.
ePub3 supports HTML5 semantic markup, CSS3 styling, MathML for equations, audio and video embedding, and full EPUB Accessibility 1.1 compliance — including screen reader support, logical reading order, and schema.org metadata. It's the format that modern institutional repositories, accessibility regulations, and distribution platforms are built around.
Reflowable ePub3 should be your default choice for any content where the text is the primary vehicle for information — and where readers benefit from controlling how they consume it.
What is Fixed Layout ePub?
Fixed Layout ePub (FXL) locks every element — text, image, and graphic — to an exact pixel position on a fixed canvas. Every page looks identical regardless of the device or reading app. It's essentially a paginated interactive PDF with ePub metadata.
This gives designers complete control over the visual presentation, but at a significant cost: the content does not reflow, does not respond to font size changes, and is extremely difficult to make accessible to screen reader users. On a small phone screen, the fixed canvas simply scales down — often making text uncomfortably small.
The Decision Framework
Choose Reflowable ePub3 when:
- Your content is primarily text — novels, academic monographs, non-fiction, educational prose
- You need EPUB Accessibility 1.1 compliance (required under the European Accessibility Act from 2025)
- Your readers use a variety of devices and screen sizes
- You distribute through Amazon KDP, Kobo, or institutional repositories
- Your content includes equations, tables, or structured data that benefit from semantic markup
- You want a single file that works across all major platforms without adaptation
Choose Fixed Layout ePub when:
- Visual design is inseparable from content — children's picture books, graphic novels, art books
- Page-by-page reading is intentional and desirable — cookbooks, illustrated reference works
- Your content was designed with specific page geometry that must be preserved exactly
- You distribute primarily through Apple Books or Amazon KDP, which handle FXL well
- Your readers are primarily on tablets rather than phones or eReaders
The accessibility trap to avoid
Many publishers choose Fixed Layout for illustrated content and then discover their institutional clients require WCAG 2.1 compliance. FXL accessibility is genuinely difficult — it requires per-page reading order declarations, extensive aria-label annotations, and alt text for every visual element. Budget for this work explicitly if you choose FXL for a market where accessibility matters.
Can you have both?
Yes — and for many illustrated titles, you should. A reflowable ePub3 edition handles institutional, accessibility, and broad device distribution. A Fixed Layout edition handles premium retail through Apple Books and Amazon KDP for readers who want the designed reading experience. The additional production cost is typically 30–40% of the original conversion cost, and the commercial return on having both editions is almost always positive for illustrated content with a trade audience.
What about Kindle?
Amazon KDP accepts ePub3 (which it converts to its internal KFX format) and also supports its own Fixed Layout specification. For reflowable content, submitting a well-formed ePub3 file produces excellent results across the Kindle ecosystem. For Fixed Layout, Amazon's own KPF format gives the most reliable output — particularly for children's books — though ePub3 FXL is also accepted.
If you're distributing exclusively through Amazon and your content is Fixed Layout, it's worth getting a KPF test conversion early in the project to catch any rendering issues before final delivery.
