.stl

What is a .stl file?

STL is a 3D model format that describes surfaces as triangle meshes — the universal input format for 3D printers and slicing software.

Safe format
Type Cad
By 3D Systems
MIME model/stl

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What is it

You designed a 3D model and need to print it. The file you export is an STL. Every 3D printer slicer — Cura, PrusaSlicer, BambuStudio, all of them — accepts STL as input. It's been the universal language of 3D printing since the technology was invented.

STL describes a 3D object's surface as a mesh of triangles. Nothing else. No colour, no texture, no material information, no units, just geometry. This extreme simplicity is both its strength (everything supports it) and its limitation (it can't describe anything beyond shape). The format dates back to 1987 and stereolithography — the original 3D printing technology. The newer 3MF format supports colour, materials, metadata, and multiple objects in a single file, and the industry is slowly adopting it. But STL's dominance shows no signs of fading.

Cura (free), PrusaSlicer (free), and BambuStudio (free) all open STL for print preparation. Blender (free) opens and edits STL meshes. Windows 3D Viewer displays them. Every CAD program (Fusion 360, SolidWorks, FreeCAD) exports STL. If someone asks you for a 3D-printable file, they mean an STL.

Technical details
Full Name
Stereolithography / 3D Printing File
MIME Type
model/stl
Developer
3D Systems
Magic Bytes
N/A
Safety
.stl is a known, safe format.
What opens it
Cura
FREE All
PrusaSlicer
FREE All
Blender
FREE All
Windows 3D Viewer
FREE Windows
FAQ
What's the difference between STL and OBJ?
STL stores only geometry (triangle mesh). OBJ supports textures, materials, and vertex colours. For 3D printing, STL is standard. For rendering and animation, OBJ is more useful.
How do I view an STL file?
Windows 3D Viewer (built-in on Windows 10/11) opens STL files. On any platform, use the free online viewer at viewstl.com, or open in Blender (free) or any slicer software like Cura.
What's the difference between STL and 3MF?
3MF is the modern replacement — it supports colour, materials, multiple objects, and metadata in a smaller file. STL is simpler and universally supported. Most slicers accept both, but 3MF is technically superior.
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