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 Does the STL File 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.

Why Use the STL File Format?

STL files are used because they are versatile, simple to create and edit, and supported by nearly all 3D printers. They are ideal for 3D printing due to their focus on surface geometry, which is the primary concern in this field.

What Are the 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.

What Are the 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 Does an OBJ File 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.

Why Use the OBJ File Format?

OBJ is favored for its ease of export and conversion to other file formats, simplifying compatibility across various software platforms. Its capability to integrate intricate texture data, including multi-color information, proves invaluable for 3D printing tasks requiring precise color detailing. This versatility makes OBJ a prime choice in industries such as entertainment, manufacturing, and design where diverse visualization needs are prevalent. 

What Are the Disadvantages 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.

What Are the 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.

Does OBJ Support 3D Color While STL Focuses on Geometry?

Yes. OBJ files are adept at handling 3D color and storing comprehensive texture details, including a spectrum of colors. This feature is essential for multi-color 3D printing, as accurate color representation improves the produced object's visual authenticity. STL files can only capture a model's geometric features, unlike OBJ files. Their limited applicability in situations where color is an important characteristic of the final printed product stems from their inability to encode texture or color data. Because of this, the OBJ file format has a clear advantage in situations where color accuracy is important for 3D printing.

Is STL a More Suitable File Format for 3D Printing Than OBJ?

It depends. STL files are often the preferred choice for 3D printing due to their streamlined nature, which focuses solely on an object's surface geometry. They offer simplicity, smaller file sizes, and widespread compatibility with 3D printing software. However, OBJ files provide more versatility by preserving additional information such as texture mapping and precise mesh encoding. While STL is ideal for quick sharing and printing, OBJ is better suited for projects requiring detailed texture data or collaborative modifications.

What Is the Difference 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:

1. Geometry Representation:

• OBJ: Can represent complex geometries using polygons and freeform curves.
• STL: Encodes the surface geometry into a triangular mesh, approximating smooth surfaces with triangles.

1. Detail and Texture:

• OBJ: Supports detailed texture information, including colors, which is essential for multi-color 3D printing.
• STL: Focuses solely on geometry and does not contain color or texture information.

1. Flexibility:

• OBJ: 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: 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.

1. Popularity in 3D Printing: 

• OBJ: Less commonly used in 3D printing compared to STL.
• STL: More popular due to its simplicity and the fact that it provides the resolution that 3D printers can handle.

1. File Size:

• OBJ: Can have larger file sizes due to the inclusion of more detailed information.
• STL: Generally smaller file sizes, making them quicker to process and easier to handle.

What Are the Factors To Consider When Choosing Between STL and OBJ for 3D Modeling Software Compatibility?

When deciding between STL and OBJ for compatibility with 3D modeling software, consider the end use, the capabilities of the software, and the model's complexity. With its widespread support among 3D printers, STL is perfect for basic models that lack color or texture. More sophisticated 3D software supports OBJ better for detailed models with colors and textures. Choose the best format by evaluating the printer's specifications and the final print quality you want.

How Do You Choose Between OBJ and STL File Formats?

Choose STL if you need a file that is simple, widely supported, and suitable for 3D printing. Choose OBJ if your project requires detailed textures, colors, or complex geometries.

Does the OBJ File Format Handle More Complex and Detailed 3D Models Than STL?

Yes, OBJ files can handle more complex and detailed 3D models than STL because they support a wider range of geometries and include color and texture information. In contrast to STL files, which can only describe surfaces with triangle facets, OBJ files may describe complicated surfaces using a variety of shapes. This covers surfaces, free-form curves, and polygons (which have more than three sides).

Is It Easy To Convert STL Files to the OBJ File Format?

The conversion process from STL to OBJ can be straightforward with the right tools, which are available online and can handle the conversion without significant loss of detail. However, the complexity of the process can vary depending on the specifics of the 3D model. Converting STL to OBJ can be complex due to model intricacy, large file sizes, and the absence of color and texture data in STL files. Software compatibility and the original file's integrity also affect the conversion difficulty. Tools can simplify the process, but results vary based on these factors.

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.

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