How to open STL, OBJ and 3MF files on Android (no CAD app needed)

Someone sends you an STL file to print, you download a model from Thingiverse or Printables, or a client shares a GLB for a product page. On a computer you’d open it in a slicer or Blender. On a phone, most file managers just say they can’t open it.

Folders has a 3D viewer built in. It opens 29 model formats, including the ones people search for most: STL, OBJ, 3MF, GLB, glTF and FBX. It’s free and works offline.

A 20 MB 3MF file with almost two million triangles, turning in Folders on Android.

Open a 3D model in three steps

1. Install Folders from the download section and allow it to see your files.
2. Find the model. Downloads usually land in the Download folder. You can also use search at the top of any folder and type part of the name, or .stl.
3. Tap the file. It opens in the 3D viewer. A large model shows a progress bar while it’s processed; then it appears on a ground grid.

If the model came from another app (a chat, an email or a cloud drive), choose Open with → Folders and it opens the same way.

Move around the model

• Drag with one finger to turn it.
• Pinch to zoom in on details, or out to see all of it.
• Double-tap to frame it again if you get lost.
• Auto-rotate (the circular arrow at the top) turns it slowly so you see every side. It’s how the video above was made.

Check it before you print

3D-print files often come in different orientations, and some details only show up when you look closely. The viewer helps with both:

• Z axis is up. Many printing tools treat Z as up, others Y. If a model lies on its side, flip this switch in Details & controls.
• Wireframe shows the triangles under the surface, handy for spotting broken or very dense areas.
• Ground grid and axes give you a sense of scale and direction.
• Details lists meshes, vertices, triangles, materials, textures, animations and the size of the model (in the model’s own units).

The dragon above, for example, has 1,908,641 triangles and measures 395 × 489 × 452 units. That tells you at a glance whether a file is a light game asset or a heavy, high-detail print.

Animations and screenshots

Animated GLB and FBX files can play their clips: open Animations, pick one, or play them all together. When you have the angle you want, Save screenshot keeps a picture of the model, which is handy for sharing a preview with someone who doesn’t have a 3D viewer.

Which 3D formats does it open?

Kind	Formats
3D printing	STL, 3MF, AMF, OBJ, G-code
Scenes and games	GLB, glTF, FBX, DAE (Collada), 3DS, MD2, LWO
USD scenes and AR models	USDZ, USDA, USDC
Point clouds and scans	PLY, XYZ, PCD, VTK, VTP, OFF
Other tools	Blender (.blend), Rhino (.3dm), VRML/WRL, MagicaVoxel (.vox), Draco (.drc), KMZ

That’s the same list the app itself uses, so if a format is in the table, it opens. You can check any other extension in the file type search.

Questions people ask

Do I need an internet connection? No. The model is read and drawn on your phone.

Will a big model work on an older phone? Usually, but very heavy files (millions of triangles) take longer and need more memory. If a phone struggles, try the file on a computer: Folders’ 3D viewer works the same way on Windows and Linux.

Can I edit the model? No, the viewer is for looking and checking, not modelling. For changes, use a slicer or a 3D editor.

Can I open models that are inside a ZIP? Yes. Tap the ZIP, then tap the model inside it. More on that in how to open ZIP, RAR and 7z files on your phone.