STLPalAll tools / MTL viewer
MTL file viewer
An MTL file holds the colours for an OBJ model. Drop it here to list every material and texture, or drop the OBJ, MTL and images together to see the model in colour.
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What is an MTL file?
MTL stands for Material Template Library. It's the plain-text file that goes with an OBJ model and says what each part looks like. The OBJ has the shape; the MTL has the colours.
The OBJ points to it with a line like mtllib model.mtl, and each part says which material it uses with usemtl. The MTL then lists those materials one by one.
What the lines in an MTL mean
| Line | What it sets | Example |
|---|---|---|
| newmtl | Starts a material and names it | newmtl Wood |
| Kd | Base colour, red green blue from 0 to 1 | Kd 0.8 0.5 0.2 |
| Ka / Ks | Ambient colour / shine colour | Ks 0.5 0.5 0.5 |
| Ns | How sharp the shine is, 0 to 1000 | Ns 120 |
| d (or Tr) | How solid it is. 1 is solid, 0 is see-through (Tr is the reverse) | d 1.0 |
| map_Kd | Image used as the colour texture | map_Kd wood.png |
| map_Bump / bump | Image used for bumps | map_Bump wood_bump.png |
Lines starting with # are comments. Apps add their own extras (like PBR lines from Blender); viewers skip what they don't know.
Why the colours don't show up
- The MTL isn't next to the OBJ, or has a different name than the mtllib line says. Keep them in the same folder with the name the OBJ expects.
- The texture paths point to the artist's computer, like C:\Users\Sam\wood.png. Edit the map_Kd line to just wood.png and put the image beside the MTL.
- The textures are TGA or DDS files. Many apps and browsers can't show those. Convert them to PNG and change the file names in the MTL.
- The usemtl names in the OBJ don't match the newmtl names in the MTL. This page tells you when they don't.
How it works
- 1Drop the .mtl file. You get every material, its colour and the textures it asks for.
- 2Drop the .obj, .mtl and texture images together to see the model with its colours.
- 3Spin and zoom the model. Missing textures are listed so you know which files to find.
Questions people ask
Checked October 2026
- Do my files get uploaded?
- No. Everything runs in your browser. The file never leaves your computer, so it works for client files and unreleased designs too.
- What is an MTL file?
- MTL (Material Template Library) is the small text file that goes with an OBJ. It names each material and sets its colour, shine and transparency, and lists the image files used as textures.
- How do I open an MTL file?
- Drop it on this page, or open it in any text editor since it's plain text. To see it on the model, open the OBJ in Blender, or drop the OBJ and MTL here together.
- Why is my OBJ still grey with the MTL?
- The material names in the OBJ (usemtl lines) have to match the newmtl names in the MTL, and the textures have to be dropped too. We point out a mismatch or a missing image.
- Does a 3D printer use the MTL?
- No. Slicers read the shape only. If you print in one colour, you only need the OBJ. For a multi-colour print, paint the model in Bambu Studio or PrusaSlicer.
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