STL vs. OBJ: What Are the Differences?

Both STL and OBJ files are widely used formats in the field of 3D printing and modeling, and each has specific functions and applications. STL (standard tessellation language), the most common,  is highly compatible and straightforward when it comes to describing three-dimensional objects with a triangular mesh. They cannot store any information about texture, color, or material. File sizes are relatively small, and STL files are widely used for simple 3D printing jobs.

However, OBJ (Wavefront object) files can be a better choice when rendering is required, since they can contain not just the surface geometry data, but also additional information such as texture and color. They use multiple polygon shapes, lines, and curves to produce a more accurate representation of a three-dimensional object than an STL file. The preferred method depends on the application and what information is needed to execute a 3d printing. Figure 1 shows a representation of OBJ on the left and STL on the right: 

This article will discuss the differences between STL and OBJ files in terms of how they work, their purposes, their advantages, and their disadvantages.

What is an STL File?

An STL file is a file saved in a format native to stereolithography CAD software created by 3D Systems. It describes a triangular mesh representing the model’s surface using a three-dimensional Cartesian coordinate system. STL files contain no scale information, and the units are arbitrary. They describe only the surface geometry of a three-dimensional object without any representation of color, texture, or other common CAD model attributes.

How STL Files Format Work

STL files use a set of triangles to represent the surface geometry of three-dimensional objects.  Three vertices expressed in Cartesian coordinates define each triangle in the mesh. Each triangular facet is also associated with a vector normal to its surface which signifies the orientation of the triangle. Since color and texture information is often not needed for 3D printing, simple STL files are often used for these applications.

Advantages of the STL File Format

Here are six advantages of the STL file format:

1. Universally Recognized: STL is widely accepted and supported by almost all 3D printers, making it a reliable choice for 3D printing projects.
2. Simplicity: The format is straightforward, focusing solely on the surface geometry of models, which simplifies the printing process.
3. Ease of Use: Due to their simplicity, STL files are easy to create, handle, and process with 3D software and machines.
4. Speed: Processing STL files is faster because of their simplicity and lack of additional data like texture and color. This leads to quicker preparation times for printing.

Disadvantages of the STL File Format

The STL file format, commonly used in 3D printing, has several disadvantages, including:

1. Lacks Texture and Color Data: STL files only contain information about the geometry of the model and do not include any data on color, texture, or materials.
2. Difficult to Modify: Once created, STL files are very hard to edit or modify.
3. Limited Detail: High-resolution models can become very large, as the detail is dependent on the number of triangles used.
4. Potential for Errors: STL files can have issues with gaps and overlaps if the model surfaces are not drawn correctly.
5. Outdated Format: The STL format has not seen significant updates since its creation, which can limit its functionality compared to newer formats.
6. May Become Obsolete: As more modern formats gain traction among users, there's a risk that STL could become obsolete, potentially causing compatibility issues and limiting access to designs stored in this format.

What is an OBJ File?

An OBJ file is a versatile 3D model format used in computer graphics and 3D printing. It encompasses geometry, texture, and material properties, facilitating accurate representation. OBJ supports precise surface encoding, including NURBS (Non-Uniform Rational B-Splines) patches for smoother surfaces, albeit leading to larger file sizes. Particularly useful for 3D scanning, it can integrate photographic information for full-color 3D printing. While other formats like AMF and 3MF may be preferred for certain printing techniques, OBJ is widely supported in various software, making it popular in game development, animation, and beyond.

How OBJ Files Work

An OBJ file works by providing a detailed representation of a 3D object. It includes data on vertices, texture coordinates, vertex normals, and the faces that make each polygon. This information is used by 3D graphics programs to reconstruct the object's surface geometry, color, shading, texture, and material. When compared to STL files, OBJ files are more versatile because they can include several kinds of extra information.

Advantages of the OBJ File Format

Here's a list of the advantages of the OBJ file format:

1. Widely Supported: Nearly every 3D software package supports the OBJ format.
2. Separate Position, UV, and Normal Topologies: Allows for the storage of different topologies, optimal for high-quality modeling tools. In 3D modeling, "UV" stands for the horizontal (U) and vertical (V) axes on a 2D texture map. These coordinates allow for precise mapping of textures onto 3D models.
3. Scalable Vector File: The objects defined are scalable without a maximum file size.
4. Supports Texturing, Colors, and Material Definition: Enables encoding of detailed textures, materials, and colors for 3D models.
5. Preserves Original Mesh and Texture: Ideal for high-resolution and full-color printing needs.

Disadvantages of the OBJ File Format

The OBJ file format, while popular, has several disadvantages including:

1. Slow and Inefficient: Being text-based, it's not space-efficient and can be slow to process, especially with large amounts of data.
2. No Scene Information: OBJ files do not support scene information or animation, limiting their use in more complex 3D projects.
3. Orphaned Technology: The format hasn't been updated since its creation in the 1980s, making it outdated compared to newer formats.
4. Post-Processing Required: The OBJ format's drawbacks include post-processing for game engines, requiring unification of topologies and conversion to triangles. This adds complexity and time to workflows, impacting efficiency, especially for large, complex models where text-based formats are less space-efficient and slower to process.

Differences Between the OBJ and STL File Formats

The OBJ and STL file formats are both used in 3D modeling and printing, but they have distinct differences:

Geometry Representation

OBJ files can represent complex geometries using polygons and freeform curves. While STL files encode the surface geometry into a triangular mesh, approximating smooth surfaces with triangles.

Detail and Texture

OBJ files support detailed texture information, including colors, which is essential for multi-color 3D printing. While STL files focuse solely on geometry and does not contain color or texture information.

Flexibility

OBJ supports a wider range of 3D data and is more adaptable in storing different kinds of forms. Details like surface properties, color information, texture mapping, and even the original mesh structure used to generate the item can be found in this supplementary data.

STL files are constrained to representing only the surface geometry of an object, making them less adaptable. Although they excel in 3D printing because of their straightforwardness and compatibility with printing software, they might not be optimal for tasks demanding more intricate visual detail or the retention of supplementary data beyond basic geometry.

File Size

OBJ files can have larger file sizes due to the inclusion of more detailed information. STL files generally have smaller file sizes, making them quicker to process and easier to handle.

Summary

This article presented STL and OBJ, explained each of them, and discussed their key differences. To learn more about STL and OBJ, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including 3D printing and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.