We’ve all been there. You find that cool cat model on Thingiverse — we won’t judge. You download the STL, all ready to watch the magic of having it materialize on your print bed. But the slicer complains it isn’t manifold or watertight or something like that. What a let down. Part of this is due to shortcomings in the STL file format. There’s a newer format available, 3MF, and Josef Prusa and Jakub Kočí would like you to start using it.
STL — short for stereolithography — is a simple format that just holds a bunch of triangles. If you need any information about the part — like colors or materials. Worse still, as in our hypothetical example, there are no definition about how the triangles relate so you can create “bad” STL files. Even properly formed files can be tough to work with. You might scale for inches and the file is set for millimeters, for example.
Turns out 3MF is actually a ZIP archive and it can contain lots of information. The file can contain one or more models, colors, slicing data, copyrights, images, and lots more. The ZIP file is often shorter, too because of the compression. The big deal, though, is that the file format won’t allow nonmanifest models and removes ambiguity so that everything nicely prints. If your slicer stores data into the file — as the Prusa one does — other people using the same software can grab your settings, too.
The format isn’t really that new — it appeared around 2015 — but it hasn’t seen widespread adoption yet. Prusa encourages you to upload models in 3MF even if you also add an STL copy for people who haven’t made the switch yet.
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