The Difference Between STL and OBJ

If you’re getting into 3D printing, you’ll quickly run into different 3D file formats. Two of the most common are STL and OBJ. What’s the difference between them, and which one should you use? In this article, we compare STL vs. OBJ in detail, covering the pros and cons of each. By the end, you’ll know which format is the best fit for your needs—and why.

What Is an STL File?

STL (stereolithography or standard tessellation language) is the de facto standard for consumer 3D printing. It was introduced in the late 1980s by 3D Systems as a way to describe models for stereolithography machines. An STL file only describes the surface geometry of an object, breaking it down into a mesh of tiny triangles. Each triangle is defined by three vertices and a normal vector that points outward.

STL is a stripped-down format: it captures just the object’s shape, with no colors, textures, or material data. It also doesn’t include units, so whether the numbers represent millimeters or inches depends on convention (most slicers assume millimeters).

STL files can be saved in two forms: ASCII (text) or binary. Both store the same data, but the binary version is much more compact. In practice, nearly every 3D printer and slicing software supports STL because of its simplicity. If you download models from public libraries like Thingiverse, they are typically provided in STL format. However, this simplicity also brings some limitations, which we’ll discuss soon.

What Is an OBJ File?

OBJ (often called Wavefront OBJ) is another widely used 3D file format, originally developed in the 1980s by Wavefront Technologies for their 3D graphics software. Today it has become a common format not only in computer graphics and animation, but also in 3D printing.

OBJ can store polygons with any number of vertices and even smooth mathematical curves such as NURBS (Non-Uniform Rational B-Splines), giving it the flexibility to handle complex or highly detailed models.

OBJ files can include more than just geometry. They often reference a companion .mtl file that defines colors, materials, and textures for the object’s surfaces. With this, an OBJ can carry multiple colors, mapped textures, or different materials on separate parts of a model. This is why it’s often chosen for full-color 3D printing, textured 3D scans, and visual applications like game design and AR/VR.

OBJ files are usually plain text. They list vertices, texture coordinates, and normals, then define faces by referencing those points. This structure keeps the format relatively easy to inspect or edit, though it also leads to larger file sizes and slower processing compared to binary STL.

STL vs. OBJ: What Are the Differences?

Let’s break down the key technical differences between STL and OBJ in detail.

Geometry Representation

Both STL and OBJ are polygonal mesh formats, but they treat geometry differently. STL represents every surface with triangles, so curves are always approximated by many small facets. A sphere in STL, for example, is built from hundreds or thousands of triangles. It only looks smooth when those triangles are tiny enough.

OBJ isn’t limited to triangles. It can store polygons with three or more vertices and even define smooth surfaces such as NURBS (Non-Uniform Rational B-Splines). In theory this allows exact curves. In practice, most OBJ files are still exported as triangulated meshes, and slicers convert curves into facets anyway. So while OBJ is technically more capable, for typical 3D printing the end result is usually the same as with STL, as long as the mesh resolution is high.

File Structure

An STL file is essentially a long list of triangles. In its ASCII form, each triangle is written out with three vertices and a normal vector. This means the same coordinates are often repeated. Binary STL stores the same data in a compact 50-byte format. STL files usually hold only one object, so multi-part models must be split into separate files or merged before export.

An OBJ file, by contrast, separates vertices from faces. It first lists all unique vertex coordinates, then defines faces by referencing them. This avoids duplication and makes it more efficient than ASCII STL. OBJ can also include texture coordinates, normals, and group faces into multiple named objects in a single file. This ability to handle multi-object models is one reason OBJ is widely used in graphics and complex assemblies.

Units and Scale

Neither STL nor OBJ reliably store unit information. STL is completely unitless. OBJ can sometimes include scale data, but it isn’t standardized and is often ignored. As a result, models may import at the wrong size. For example, something designed in inches can appear 25.4× too small if the slicer assumes millimeters. Most slicers default to millimeters, so it’s always best to double-check scale when importing. Newer formats like 3MF or STEP solve this by embedding units, but with STL and OBJ you’re relying on convention.

Material and Texture Support (Color vs. Monochrome)

One of the biggest differences between STL and OBJ is the ability to handle color and materials. STL files are purely geometry—no colors, textures, or material properties are saved. No matter how your model looks in CAD, once exported as STL it becomes a single, uniform mesh. This is fine for most printers that work in one color at a time, but it’s a clear limitation if you want multi-color or multi-material prints.

OBJ, on the other hand, can include rich appearance data. Alongside the .obj file there is usually a .mtl file, and sometimes texture images, which together define how the model looks. This means OBJ can carry solid colors for different parts or full texture maps, making it the go-to choice for full-color 3D printing and for sharing textured 3D scans. High-end printers and scanners in fields like art and dentistry often rely on OBJ for this reason. The only catch is that textures aren’t embedded. When sharing an OBJ you need to include the .obj, .mtl, and image files together—zipping them is the easiest way to avoid missing files. Despite that, OBJ remains the better choice when appearance matters, while STL is usually all you need for single-material parts.

File Size and Efficiency

ASCII STL is the least efficient because it repeats vertex coordinates for every triangle. This makes detailed models bulky fast. Binary STL is much better—each triangle is stored in a fixed 50-byte block, so file size scales directly with triangle count and usually stays manageable. OBJ, although text-based, avoids duplication by listing each vertex once and then referencing it. This means an ASCII OBJ can actually be smaller than an ASCII STL of the same mesh. For pure geometry, binary STL and OBJ end up about the same, with ASCII STL clearly the outlier.

When OBJ carries materials and textures, the total package size grows because of the image files. Very large OBJs can also load more slowly than binary STLs. But in everyday use, the difference is minor. Most hobby models are only a few megabytes either way. If you just need geometry, a binary STL is compact and quick to load. If you need colors or textures, OBJ is worth the extra size. And in both cases, compressing the files into a ZIP shrinks them dramatically, so storage or sharing is rarely a problem.

Software Compatibility and Support

STL is the default for 3D printing—every slicer accepts it, and repositories like Thingiverse mostly distribute STL files. OBJ is also supported by modern slicers and is useful when models contain multiple parts or colors. In CAD programs such as Fusion 360 or SolidWorks, STL is the standard export for printing. Digital tools like Blender or Maya often use OBJ, especially when the model needs to keep colors or materials.

Outside of printing, STL sees little use in graphics, while OBJ is still a common exchange format in games, animation, and AR/VR. Printing services typically default to STL for single-color jobs but may request OBJ for full-color or multi-material prints. Both formats convert easily in tools like MeshLab or Blender, so you won’t be locked in.

Pros and Cons of STL and OBJ

We’ve covered the main technical differences between STL and OBJ. Now it’s time to step back and see the overall picture. Each format has its strengths in certain situations and limitations in others. To make the comparison clearer,let’s summarize the key pros and cons of STL and OBJ, especially for 3D printing.

Which Format Should You Use for 3D Printing?

For most 3D printing projects, especially if you’re a beginner, STL is the safe default. It holds just the geometry, works on every printer and slicer, and keeps the workflow simple.

However, there are scenarios where OBJ might be the better choice:

Full-color or multi-material printing: OBJ preserves vertex colors, textures, or multiple shells in one file. This is useful for color-capable printers or multi-material setups (e.g., dual-extruder machines).

3D scanning with textures: Scanned models often include detailed surface colors. Saving as OBJ keeps those textures intact, making them useful for both viewing and full-color printing.

Multi-part assemblies: An OBJ can store several parts in a single file, aligned in their correct positions. This simplifies slicing for dual-material or multi-component designs.

Dual-use: If a model is used both for printing and for rendering or game engines, OBJ can carry material and geometry in one file, avoiding duplicate exports.

Large ASCII meshes: In rare workflows where only ASCII is used, OBJ may be smaller than ASCII STL due to vertex referencing (though binary STL is usually better here).

It’s worth noting that there are newer file formats purpose-built to overcome STL’s limitations (like AMF and 3MF for 3D printing). 3MF, for example, can include color, materials, multiple objects, and units, all in one compact file.

Conclusion

This article introduced STL and OBJ, explained their core features, and compared their strengths and limitations for 3D printing. Both formats remain widely used, and understanding when to choose STL or OBJ can help you streamline your workflow and get better results.

At Chiggo , we provide a full range of custom manufacturing services, including 3D printing, CNC machining, injection molding, and more. Whether you need rapid prototypes or production parts, our team can support your project from design to delivery. Contact us today or upload your CAD file for a free, no-obligation quote.