3MF to STL: binary vs ASCII
Both are valid STL, but they behave very differently. Here is exactly when to pick each one when you convert 3MF to STL — and how to spot which file you already have.
Drop .3mf files here
or drag & drop — up to 150 MB each, multiple files supported
The short answer
Choose binary STL for almost everything. It is compact, loads instantly and is what Cura, PrusaSlicer, Bambu Studio, Simplify3D and almost every repair tool expect. Choose ASCII STL only when a specific pipeline demands plain text — an archive, a code review, or a tool that refuses binary input.
How the two formats differ
- Binary STL: an 80-byte header, a triangle count as a uint32, then 50 bytes per triangle (normal + three vertices as five floats). Dense, unreadable, fast.
- ASCII STL: the word
solid, then a human-readablefacet normal/outer loopblock per triangle with values printed as decimal text. - Size: for the same mesh, ASCII is roughly five times larger than binary because every coordinate is spelled out.
- Geometry: identical. The conversion is lossless either way — you are choosing an encoding, not a quality setting.
When ASCII genuinely earns its size
- You are putting the model in version control and want readable diffs.
- A mesh repair or analysis tool only ingests text.
- You need to inspect or hand-edit a single triangle line.
- You are shipping the file somewhere that cannot handle binary attachments.
What gets lost either way
STL has no colour, no material list and no texture. When you convert 3MF to STL, every painted surface collapses into geometry with one material slot. That is fine for mono-material printing, and it is exactly why 3MF became popular: it keeps the colour story that STL cannot.
Rule of thumb: default to binary, switch to ASCII, download, and if your slicer complains about encoding, switch back — the conversion takes seconds and nothing is uploaded either time.
Pick your slicer route
The format decision is the same across tools, but the workflow differs a little. Compare our Cura guide, the Bambu Lab route and the PrusaSlicer notes, or read the 3MF to STL troubleshooting hub if something went wrong.
Frequently asked
Which STL should I download when I convert 3MF to STL?
Binary — it is about five times smaller, loads faster and is the default in every slicer. Use ASCII only when a tool demands plain text.
How do I tell binary from ASCII STL by eye?
Open it in a text editor. ASCII starts with "solid" and readable numbers; binary shows garbage characters because floats are stored as raw bytes.
Does converting 3MF to STL lose colour?
Yes. STL stores geometry only, so colours, textures and materials are dropped. Assign colour per object in your slicer afterwards.
Is binary STL always smaller than the 3MF?
Usually — the 3MF archive also holds thumbnails and textures. For simple geometry with heavy textures the 3MF can be the larger of the two.