An OBJ file stores the shape and appearance of a 3D object

An OBJ file is a text document that describes a three-dimensional shape — where its corners are, what surfaces connect them, and what colors or textures cover those surfaces. Think of it as a blueprint that tells 3D software (or a video game, or a 3D printer) how to draw or build something in three dimensions.

The file itself is plain text, which means you can open it in Notepad and read it, though it will look like a long list of numbers and coordinates. Those numbers represent points in 3D space. When a program reads the file, it connects those points to form the shape you see on screen.

OBJ files are one of the oldest and most widely supported 3D formats. They were created by Wavefront Technologies in the 1980s for use in their animation software, but they became so common that almost every 3D program today can read them. This makes OBJ a safe choice if you need to move a 3D model between different software programs.

Key Takeaways

  • An OBJ file is a text-based description of a 3D shape, including the location of its corners and the surfaces that connect them.
  • OBJ files are widely supported across different 3D software, making them useful for sharing models between programs.
  • You can open an OBJ file in a text editor and see the raw data, though the numbers will not make sense without 3D software to visualize them.
  • OBJ files often come with a companion MTL file that describes colors, textures, and how surfaces should reflect light.

What information an OBJ file actually contains

An OBJ file breaks a 3D shape into its basic parts. The most important part is the list of vertices — these are the corner points of the shape, each one defined by three numbers representing its position in 3D space (X, Y, and Z coordinates). If you are building a straightforward cube, you would have eight vertices, one for each corner.

The file also lists faces, which are the flat surfaces that connect those vertices. A face tells the software which vertices to connect with lines to form a surface. For a cube, you would have six faces (the top, bottom, and four sides). The software uses these faces to know which surfaces to draw and how to shade them so they look three-dimensional.

Many OBJ files also include information about texture coordinates, which tell the software where on a 2D image (like a photograph) each point of the 3D surface should pull its color from. This is how a flat picture of wood grain or brick can be wrapped around a 3D object to make it look realistic.

When you will encounter OBJ files

OBJ files appear in several common situations. If you read a 3D model from a website — whether it is a character for a game, a part for a 3D printer, or an object for animation — it will often be in OBJ format. Video game developers use them during the creation process, though the final game usually converts them to a faster format.

3D printing is another common place. When you send a design to a 3D printer, the software often accepts OBJ files as input. Architects and product designers use OBJ files to share models with colleagues or clients. If you use 3D modeling software like Blender, Maya, or even free tools like Tinkercad, you can save your work as an OBJ file and open it in almost any other 3D program.

How OBJ files relate to MTL files

An OBJ file often comes with a companion file called an MTL file (material file). While the OBJ file describes the shape, the MTL file describes how that shape should look — its color, shininess, transparency, and what textures to use. The OBJ file contains a reference to the MTL file, so when you open the OBJ in 3D software, the program knows to look for the MTL file to get the appearance information.

If you read a 3D model and it comes as a folder with multiple files, you will usually see both the OBJ file and the MTL file inside, along with image files (like JPG or PNG) that contain the actual textures. All of these files need to stay together in the same folder for the model to display correctly. If you move just the OBJ file to a different location, the software will not be able to find the textures and the model will appear as a plain gray shape.

Why OBJ remains common despite newer formats

Newer 3D file formats exist — FBX, GLTF, and others — that can store more information and work more efficiently. But OBJ remains popular because it is straightforward, widely supported, and has been around long enough that almost every 3D program can read it. If you need to move a model between different software, OBJ is often the safest choice because you know both programs will understand it.

The simplicity of OBJ is also a limitation. It cannot store animations, bones (the internal structure that lets a character move), or some advanced material properties. For those features, you would need a more complex format. But for static 3D shapes — objects that do not move or change — OBJ works well and remains the standard.

How to open and view an OBJ file

To see what an OBJ file actually looks like, you can open it in any text editor (Notepad on Windows, TextEdit on Mac, or any other plain-text program). You will see lines starting with letters like "v" (for vertex), "f" (for face), and "vt" (for texture coordinate), followed by numbers. This is the raw data that describes the shape.

To actually see the 3D shape rendered on screen, you need 3D software. Free options include Blender (a full 3D modeling suite), Tinkercad (a simpler browser-based tool), or even online OBJ viewers that let you upload the file and rotate it in your browser. Most 3D software can open OBJ files directly — just use File > Open and select the OBJ file.

Frequently Asked Questions

Can I edit an OBJ file in a text editor?

Technically yes, but it is not practical. You could open the file in Notepad and change the numbers, but you would have no way to see the results without opening it in 3D software. Any small mistake in the numbers will break the file. It is much easier to use 3D software to make changes and then save as OBJ.

What happens if I lose the MTL file that came with an OBJ?

The OBJ file will still open and display the shape, but it will appear as a plain gray or white object without colors or textures. If you have the image files (the textures), you can create a new MTL file or use 3D software to reapply the textures. If you only have the OBJ file, you have lost the appearance information permanently.

Can I 3D print an OBJ file directly?

Most 3D printers accept OBJ files, but the printer software may first convert it to a format called STL (which is optimized for printing). You typically upload the OBJ to the printer's software, which handles the conversion. Check your printer's documentation to see which formats it supports.

Is an OBJ file the same as a model?

An OBJ file is one way to store a 3D model, but a model can be stored in many different file formats. OBJ is just one option — FBX, STL, GLTF, and others all store 3D models. Think of OBJ as one container type among many.