Understanding 3D File Formats

When looking for models to print, you may have noticed that model files come in different file extensions like .stl, .obj, or .3mf. This guide breaks down what these file types actually mean and which ones you should use for your 3D printer.

What File Formats Will You Actually See?

When you download models from sites like Thingiverse, MyMiniFactory, Cults, or Printables, most of the files you encounter will be STL files (about 95% of the time). You might occasionally see 3MF or OBJ files. Here's what each one means.

STL Files: The One You'll Use Most

STL (.stl file extension) is the standard file format for 3D printing. If you're downloading a model to print, there's a high chance that it'll be an STL file. Every 3D printer and slicing software (programs like Cura, PrusaSlicer, or Bambu Studio that prepare your models for printing) can read STL files, which is why creators use them and distribute them in this format online.

An STL file contains the shape of the model. It's basically the 3D geometry that tells your printer what to print using filament. It's made up of thousands of tiny triangles that form the surface of the object.

STL files are pretty basic. They don't include colors, textures, and lack other fancy details. They're just shapes. That's why if you see a bright red vase in the preview or thumbnail image, the actual STL file doesn't know it's supposed to be red. That's just how the creator chose to show it for their model.

For most people printing at home, STL files are all you need to get started. They're simple, they work, and you won't have any compatibility issues. You'll find STL files on every popular 3D model site like Thingiverse, Printables, MyMiniFactory, Cults, and more.

3MF Files: The New Kid

3MF (.3mf file extension), also known as 3D Manufacturing Format, is a newer format that's trying to replace STL. It was developed by the 3MF consortium, including Microsoft and a bunch of 3D printing companies, to fix some of STL's limitations. A 3MF file can include colors, materials, and even print settings, all in a smaller file size than OBJ.

The catch is not every slicing program supports it yet. Most modern slicers like PrusaSlicer, Cura, and Bambu Studio can handle 3MF files, but if you're using older software, you might run into issues.

If you see a model available in both STL and 3MF, try 3MF if your slicer supports it. Otherwise, just grab the STL. As creators begin sharing their models in this format, you'll start seeing more 3MF files on Printables and other modern platforms as the format gains popularity.

OBJ Files: When You Want More Detail

OBJ (.obj file extension) files are similar to STL, but can include extra information like colors and textures. You might see these for more complex models, especially if someone scanned a real object or created something with multiple colors.

One of the downsides of OBJ files is that they are bigger in size. They take up more space on your computer and sometimes your slicing software (like Cura or PrusaSlicer) might not handle them well or perfectly. If you have a multi-color printer (think Prusa XL or Bambu Lab printers with AMS) or you're printing something that benefits from seeing the textures, OBJ files can be useful.

You might occasionally find OBJ files on sites like MyMiniFactory or CGTrader, particularly for artistic models or scanned objects. The truth is that most people stick with STL as it is supported by more slicing software.

What About All Those Other Formats?

You might occasionally come across other file types like PLY, STEP, IGES, or AMF. The reality is that unless you're doing something more specialized, you probably don't need them.

PLY files (.ply) are often used for 3D scans. STEP (.step or .stp) and IGES (.iges or .igs) are engineering and CAD formats you'll rarely see on popular 3D model sites. AMF (.amf) tried to be a better STL but never really caught on.

For everyday 3D printing from sites like Thingiverse, Printables, or MyMiniFactory, you can safely ignore these unless you have a specific reason to use them. Stick with STL, OBJ, or 3MF as those are what you'll actually encounter most of the time.

Which Format Should You Download?

When you find a model and go to download it, you'll usually see a few options. Here's what to do:

If there's an STL file available, download that one. It's the safest choice and will work with any printer and slicer. This is what you'll find 95% of the time on Thingiverse, Printables, and similar sites.

If the creator only offers 3MF and your slicer is fairly new, go ahead and try it as this file format will include colors which are useful for multi-color prints. Printables often includes 3MF files alongside STL if you look under the Files tab.

Only download OBJ files if you specifically need the color or texture information or if that's the only format available. You'll see these more often on sites focused on artistic or scanned models.

Most of the time, creators make their models available as STL files because they know that's what everyone needs.

Do You Ever Need to Convert Files?

Sometimes you'll download a file and your slicing software (the program you use to prepare models for printing, like Cura or PrusaSlicer) won't open it. This doesn't happen often, but when it does, you can use free tools to convert it. Programs like Meshmixer or Blender can convert between formats, and there are also free online converters you can find with a quick search.

If you're just starting out, stick with STL files and you won't need to mess with conversions at all.

Why This Matters (And Why It Doesn't)

File formats might sound technical and intimidating, but in practice they barely matter for most people. You download an STL file, open it in your slicing software (like Cura, PrusaSlicer, or whatever came with your Ender 3 or Bambu Lab printer), adjust a few settings, and hit print. That's it!

The format is just the container for the 3D model. What actually matters is the model itself. Is it the right size? Does it need supports? Will it fit on your printer's build plate (the flat surface where things print)? Those questions are way more important than whether it's an STL or 3MF file.

Quick Cheat Sheet

STL - Standard format, works everywhere, no colors, perfect for 99% of prints

3MF - Modern upgrade to STL, smaller size, more features, not universally supported yet, but compatible with slicers such as Bambu Studio

OBJ - Has colors and textures, bigger files, only needed for specific cases

The Bottom Line

If you're just getting into 3D printing and someone asks what format you need, the answer is STL. Download STL files, print them, and don't overthink it. As you get more experienced, you might start exploring other formats for specific projects. For now, STL is your friend.

That's really all you need to know about file formats. Now go find something cool to print.