Design Files 101: STL, OBJ, and 3MF Explained

You've found the perfect 3D model online or someone sent you a design file for a custom print. You download it, and the file extension says .stl or .obj or .3mf.

What's the difference? Does it matter which one you use? Will your printer (or print service) accept all of them?

Here's a breakdown of the most common 3D file formats, what they're good for, and which one you should use when ordering a custom print.

STL – The Industry Standard

What it is: STL (STereoLithography) is the most widely used 3D printing file format. It's been around since the 1980s and is supported by virtually every slicer and 3D printer on the market.

What it stores: STL files contain only geometry – the shape of your model represented as a mesh of triangles. No color, no texture, no material information. Just the surface.

Best for:

• Single-color prints
• Functional parts
• Prototypes
• Most general 3D printing applications

Pros:

• Universal compatibility – works with every slicer
• Small file size (usually)
• Simple and reliable

Cons:

• No color or texture data
• Can produce large files for highly detailed models
• Older format with some technical limitations

When to use it: If you're ordering a custom print and the file is a single solid object, STL is your go-to. It's the safest bet for compatibility.

OBJ – The Multi-Purpose Format

What it is: OBJ (Wavefront Object) is a 3D file format originally developed for 3D graphics and animation. It's commonly used in game design, CGI, and 3D modeling software.

What it stores: OBJ files can store geometry, color, and texture information. They're often paired with an MTL (material) file that defines colors and surface properties.

Best for:

• Multi-color prints (if your printer supports it)
• Models with texture maps
• Files exported from 3D modeling software like Blender or Maya

Pros:

• Supports color and texture data
• Human-readable text format (you can open it in a text editor)
• Widely supported by 3D modeling software

Cons:

• Larger file sizes than STL
• Not all slicers handle OBJ files well
• Color/texture data is often ignored by FDM printers

When to use it: If you're working with a multi-color model or exporting from 3D modeling software, OBJ is a solid choice. Just know that most FDM printers will ignore the color data and print it as a single color anyway.

3MF – The Modern Upgrade

What it is: 3MF (3D Manufacturing Format) is a newer file format developed by the 3MF Consortium (including Microsoft, Autodesk, and others) to address the limitations of STL.

What it stores: 3MF files can store geometry, color, texture, material properties, print settings, and even multiple objects in a single file. It's basically a zip file containing all the data needed for a print.

Best for:

• Multi-material or multi-color prints
• Complex assemblies with multiple parts
• Files that include pre-configured print settings
• High-resolution models

Pros:

• Stores more data than STL (color, material, settings)
• Smaller file sizes for complex models
• Better precision and fewer errors
• Future-proof format with growing support

Cons:

• Not as universally supported as STL (yet)
• Some older slicers don't recognize it

When to use it: If you're working with a modern slicer (like PrusaSlicer, Cura 4.0+, or Bambu Studio) and want to preserve color, material, or print settings, 3MF is the way to go.

Other File Formats You Might See

These aren't as common for 3D printing, but you might encounter them:

• STEP (.step, .stp) – CAD format used in engineering. Great for precision parts, but needs to be converted to STL or 3MF for printing.
• IGES (.igs, .iges) – Another CAD format. Same deal as STEP.
• AMF (Additive Manufacturing File) – An older attempt to replace STL. Supports color and materials, but 3MF has largely replaced it.
• PLY (Polygon File Format) – Used for 3D scanning. Can be converted to STL for printing.

If you have one of these, most slicers can convert them to STL or 3MF.

Which Format Should You Use?

Here's the quick decision tree:

• Ordering a custom print? Use STL. It's the most compatible and reliable.
• Multi-color or multi-material print? Use 3MF if your printer/service supports it. Otherwise, STL and specify colors separately.
• Exporting from CAD software? Export as STEP or STL depending on whether you need precision engineering data or just the shape.
• Downloading from Thingiverse or MakerWorld? Most files are STL. Download and send it as-is.

What If Your File Won't Open?

If you're having trouble with a file, here are some common fixes:

• File won't import into your slicer? Try converting it using a free tool like Meshmixer or an online converter.
• File is corrupted or has errors? Run it through a repair tool like Netfabb Online Service (free).
• Not sure if your file is printable? Send it to us. We'll review it, fix any issues, and let you know if it's good to go.

Need help prepping your file for printing? Check out our guide: You Found the File. Now What?

Still Confused? We'll Handle It

If file formats make your head spin, don't worry. Send us whatever you've got – STL, OBJ, 3MF, STEP, or even a sketch – and we'll take care of the rest.

Submit your file for a custom print or contact us with questions. We'll make sure your file is print-ready and optimized for the best results.