Why did my textured model convert to plain grey?

Because the target format has no concept of materials. STL, PLY, OFF, 3MF, and DAE receive the geometry and drop the appearance. If you need the textures to survive, convert to GLB, glTF, or OBJ instead.

Why did I get a ZIP instead of a single file?

OBJ and glTF store materials and textures in separate sidecar files. When the model is textured, the export is packaged as a ZIP so those files arrive with the mesh — a lone .obj or .gltf would open as an untextured model, or not at all.

Which format should I use for the web or AR?

GLB. It packs the mesh, materials, and textures into a single binary file, which is exactly what model viewers and AR tools expect, and it means you have one file to hand over rather than a folder.

Why is my model the wrong size after converting?

STL and OBJ do not store units, so the receiving software has to assume one. A model exported in millimetres and read as metres is a thousand times too small. Check the bounding-box dimensions after converting, and prefer 3MF for printing where your slicer supports it.

3D Model Converter

Convert 3D models between STL, OBJ, GLB, glTF, PLY, and more. Move meshes between 3D printing, modeling, and web/AR tools — free, no signup.

Popular conversions

STL to OBJ Converter STL to GLB Converter OBJ to GLB Converter OBJ to GLTF Converter GLB to OBJ Converter

All supported formats

STL OBJ GLB GLTF PLY 3MF DAE OFF

These formats do not all describe the same thing

3D formats are unlike image or audio formats in one important way: they are not all describing the same kind of object. STL describes a surface and nothing else. OBJ describes a surface with material references. glTF and GLB describe a whole scene with hierarchy and materials. DAE adds animation.

So a 3D conversion is not lossy in the compression sense. It is lossy in the sense that the destination format may have nowhere to put half of what you had, which is why a textured model converted to STL comes back as plain grey geometry.

Format	What it carries
STL	Triangles only — no colour, no materials, no units, no hierarchy
OBJ	Geometry plus materials in a sidecar .mtl with texture images
PLY	Geometry, optionally with per-vertex colour. Scanning and research
OFF	Geometry only — a plain interchange format
3MF	Geometry plus print metadata: units, colours, multiple objects
DAE	A full scene with hierarchy, materials, and animation
glTF	A full scene for real-time delivery, with sidecar .bin and textures
GLB	The same as glTF, packed into a single binary file

How the conversion runs

Straight geometry conversions go through trimesh, which loads the mesh and re-exports it. Where materials and textures need to survive the trip — GLB, glTF, and OBJ — the job is handed to Blender instead, because carrying a material graph faithfully across formats is work a geometry library does not attempt.

OBJ and glTF both split themselves across several files: an OBJ references a .mtl which references texture images, and a .gltf references a .bin holding the geometry buffers. When a textured model is exported to one of these, the output is packaged as a ZIP so the sidecars stay with the mesh instead of arriving alone and broken. Uploading a textured OBJ works the same way round — the converter accepts the model together with its .mtl and texture files.

Check the scale before you print

STL and OBJ do not record units. A model exported in millimetres and imported into software that assumes metres is a thousand times too small, and the usual symptom is a model that seems to be missing because it is one pixel wide at the origin.

No converter can fix this, because the information genuinely is not in the file. After converting into STL or OBJ, check the bounding-box dimensions in whatever you open it with, before you print it or drop it into a scene. 3MF is the better choice where your slicer accepts it, precisely because it does carry units.

Related converters

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Frequently asked questions

Why did my textured model convert to plain grey?: Because the target format has no concept of materials. STL, PLY, OFF, 3MF, and DAE receive the geometry and drop the appearance. If you need the textures to survive, convert to GLB, glTF, or OBJ instead.
Why did I get a ZIP instead of a single file?: OBJ and glTF store materials and textures in separate sidecar files. When the model is textured, the export is packaged as a ZIP so those files arrive with the mesh — a lone .obj or .gltf would open as an untextured model, or not at all.
Which format should I use for the web or AR?: GLB. It packs the mesh, materials, and textures into a single binary file, which is exactly what model viewers and AR tools expect, and it means you have one file to hand over rather than a folder.
Why is my model the wrong size after converting?: STL and OBJ do not store units, so the receiving software has to assume one. A model exported in millimetres and read as metres is a thousand times too small. Check the bounding-box dimensions after converting, and prefer 3MF for printing where your slicer supports it.
Is the 3D Model Converter free?: Yes, every conversion is completely free with no account and no watermark.
Do I need to install anything?: No. Use the tool from your browser; files are uploaded to our servers for processing.
Are my files safe?: Files are auto-deleted after 2 hours and are never shared.