Will ASCII print more accurately?

No. Accuracy comes from the mesh and the unit scale, not from spelling numbers out as text. ASCII and binary can describe the same corners. Binary is smaller.

When should I turn on ASCII?

When you want to open the STL in a text editor and read a few facets, or when a very old tool rejects binary. For Bambu Studio, Cura, and PrusaSlicer, leave binary on.

Does binary hide a bad mesh?

No. Holes and flipped faces are in the triangles either way. Binary is only a packing format.

Binary vs ASCII STL: Which Should You Download?

Binary STL is compact and practical for most slicers; ASCII helps with inspection and diffs. Compare both, then convert OBJ to STL privately.

An STL is either compact binary or verbose text. The triangles can be identical. The files will not be. This converter writes binary unless you check the ASCII option, because the next app in a print workflow is a slicer, and slicers are built for the compact form.

What binary stores

A binary STL starts with an 80-byte header that most tools ignore, then a count of triangles, then each triangle as a normal and three corners in little-endian numbers, plus a 2-byte attribute that is usually zero. There is no material, no object name that slicers rely on, and no unit. The same unit rules apply as for any other STL: the numbers are whatever we scaled them to, and the slicer will call them millimeters.

Binary files grow in a straight line with the triangle count. A 12-triangle cube is a few hundred bytes. A sculpt with hundreds of thousands of triangles is still much smaller than the same data written as words. That size is why downloads and slicer imports feel quicker, and why the default is binary even though ASCII is easier to explain on a whiteboard.

What ASCII stores

ASCII STL is text. You will see solid, then a facet normal, an outer loop, three vertex lines, and endsolid. You can open it in an editor and read coordinates. That is genuinely useful when you are debugging a scale bug: search for a vertex and see whether a corner you expected at 40 is sitting at 0.04 or at 40000. It is a poor way to ship a dense mesh. The file is large, slow to write, and easy to corrupt if a program rewrites the text with a locale that swaps decimal commas.

ASCII does not preserve MTL data, and it does not make the mesh manifold. It is not a “source” format the way OBJ is. If you want something you can edit as a mesh, keep the OBJ. If you want something you can glance at as text, ASCII STL is enough for a few facets and miserable for a whole character.

Which one to download

Use binary for Bambu Studio, UltiMaker Cura, and PrusaSlicer. Use ASCII when a teaching tool, a diff, or your own eyes need text, or when you are confirming a single coordinate while you chase a unit mistake. You can convert the same OBJ twice. The triangle count should match. The bounding box should match if the unit, scale, axis, and bed options match. If those settings differ, the files differ because the geometry differs, not because one of them is binary.

The header in a binary file is not a reliable place to store the unit you chose. Do not depend on it. The bounding box on the converter, and the size reported by the slicer, are the checks that matter. Millimeters vs meters is the scale article. What STL is is the format primer underneath this comparison.

Nothing about the packing changes privacy. Binary and ASCII are both built in the worker and saved as a local Blob. Neither one is uploaded to make the other. If a file fails to open, check that you did not rename an ASCII file and expect a binary parser, or the reverse. The extension is .stl either way. When in doubt, export binary again and let the slicer read that fresh file.