Should the print file come from the textured OBJ or a clean export?

From a clean one. Slicing a textured OBJ works but wastes the material work and risks slicing artifacts from edit history. The disciplined flow is: textured OBJ as the master, a converted STL as the print artifact, regenerated whenever the master changes.

Why did my multi-part OBJ become one blob in the slicer?

OBJ groups convert to a single STL shell — the format has no object concept. If parts need separate orientation or colors, split the OBJ in a DCC first and convert each part, or arrange them in the slicer as one combined print.

My OBJ was authored in meters — will the print come out correctly sized?

The converter maps glTF-style meters to the slicer's millimeters (×1000). But OBJ itself declares no units — a 1.8-unit figure might be meters (human) or millimeters (part). Check the bounding box in the preview and scale in the slicer before committing resin.

What happens to OBJ's MTL materials in the STL?

They vanish — STL's data model is triangle positions only. Multi-material OBJs collapse to one shell; if you need color zones for multi-extruder printing, split the OBJ into per-material STLs and assign extruders per part in the slicer.

Is the STL watertight if the OBJ wasn't?

Conversion never heals: open edges, flipped normals and self-intersections pass through. DCC-authored OBJs are usually clean; laser-scanned or AI-meshed ones often aren't. Watch the preview and run mesh repair in the slicer or a DCC when it flags issues.

Do I need the MTL sidecar for an STL conversion?

No — the STL writer ignores materials entirely. Loading the .obj alone is sufficient. (Keep the .mtl handy only if you plan a GLTF/GLB output later, where materials matter.)

OBJ → STL OBJ to STL Converter — Online & Free

Change a OBJ model into STL in one pass, then see exactly what the new file keeps, flattens or drops before you download it.

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Reads GLB, GLTF, OBJ, STL, FBX, PLY

GLBGLTFOBJSTLFBXPLY

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Kept

The triangle mesh at authored resolution and scale

Lost

Materials, textures, UVs (irrelevant to slicing), groups and the .mtl packaging

Use for

Sending sculpted, scanned or DCC-edited meshes to FDM and resin printers

Using the STL file afterwards

Slice directly in Cura/PrusaSlicer/Bambu Studio; run a watertightness check first if the mesh was ever hand-edited

OBJ to STL is the last mile before manufacturing: a fully textured, editable mesh sheds its materials, colors and groups to become the bare shell every slicer wants. Shape and scale pass through untouched; everything that made the model pretty in a viewport stays in the OBJ, which is exactly why the print copy should be a separate artifact.

What changes in the file

1
Color intent is lost by design — a multi-color model becomes a mono print unless the slicer handles color separately
2
Watch units: OBJ is nominally unitless too, and slicers guess; confirm dimensions before committing resin
3
If the OBJ was scaled non-uniformly in a DCC, verify the conversion honored it — slicers do not forgive surprises

OBJ → STL: format spec comparison

Hard facts side by side — what each format is, where it comes from and what it can hold.

Spec	OBJSource format	STLTarget format
Developer	Wavefront Technologies	3D Systems (Chuck Hull, SLA inventor)
First released	1980s (Princeton Univ. lineage)	1987
Data model	Plain-text vertex/face lists + MTL sidecar	Triangle soup, ASCII or binary
Textures	UV coords only; MTL references image files	None
Animation	None	None
Typical size	Large (ASCII vertices), shrinks with -binary variants	Binary moderate; ASCII very large
Openness	Open, informal spec	Open, de-facto standard
Primary use	DCC interchange, sculpting, 3D printing prep	3D printing (FDM / SLA / SLS)

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More ways out of OBJ

OBJ → GLB OBJ → GLTF OBJ → PLY

Other routes into STL

GLB → STL GLTF → STL FBX → STL PLY → STL

Every conversion route

Per-format pages and all 25 format-to-format paths — each one pre-configures the converter for that exact job.

FAQ