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STL File Format For 3D Printing: Everything You Need to Know


What is an STL File format? How does it work with 3D printer? Have you thought why most of 3D printing model is STL file? Is there any other alternate 3d printing file available?

In this article, we will simply explain the STL file format for 3D printing in depth.

1. What Is an STL File?

STL file format is the most commonly used format file for 3D printing. An STL file is a format that describes the surface geometry of a 3D object without any color, texture, or other attributes.

This format represents the surfaces of a model with small triangles. The more complex the structure is, the more triangles will be used to get the right model.

today, since it is simple, light and easy to be handled by 3D machines and software, STL has been widely used for rapid prototyping, 3D printing, and computer-aided manufacturing.

2. What Does the File Extension .STL Stand For?

STL” is the file extension of the STL file format.

It is an abbreviation of the word ‘STereoLithography‘, sometimes refer to ‘Standard Triangle Language‘ or ‘Standard Tessellation Language‘.

3. Three Special Rules For the STL Format

3.1 Vertex to vertex rule

The vertex rule states that each triangle must share two vertices with its neighboring triangles.

This means that a vertex of one triangle must not lie on the side of another triangle.

3.2 Orientation rule

This rule states that the orientation of the facet must be defined clearly. This orientation is specified in two ways.

First, the direction of normal vector should point outwards.

Moreover, the vertices should be listed in counter-clockwise order when looking at the object from the outside (or right-hand rule).

3.2 All-positive Octant rule

This rule states that all the coordinates of the triangle vertices must be positive (nonnegative and nonzero).

The rationale behind this rule is to save space. If the 3D object was allowed to live anywhere in the coordinate space, we would have to deal with negative co-ordinates.

To store negative coordinates may require an additional bit to store a sign (+/-).

Hence, it is important to ensure that all coordinates are positive. When all the coordinates are positive, it also means that more space will be saved.

4. How Is an STL File 3D Printed?

For 3D printing, after you designed the model, the next phase is digitally slicing the STL File to get it for printing.

3D printer cannot conceptualize a 3D model in the same way as you or I.

Slicer, a piece of 3D printing software, will convert digital 3D models into printing instructions for your 3D printer to create an object.

The slicing process breaks down your STL file into many (hundreds or thousands) flat horizontal layers based on the settings you choose and calculates how much material your printer will need to extrude and how long it will take to do it.

The design STL file for each layer is then sent to the printer head to print, or lay down, in order. 

The plastic cannot be laid down in thin air, and the slicer software will add in support columns, where needed , though STL file don’t have this part design.

Once the slicer program has worked its magic, the data is then sent to the printer for the final stage. 

RELATED: Top 20 best cheap 3d printer 2020 (Starting at $99!)

5. Is Every STL File 3D Printable?

Pokemon Nessa 3D Printable Model


Even if it is the standard for 3D printing, an STL file just the container for the data , not always ready-to-print.

A model has to be closed, manifold (each triangle vertex should not be on another triangle edge) and not self-intersected.

In another words, only a 3D design that’s specifically made for 3D printing is 3D printable.

When you download an STL file that you are not sure if it’s made for 3D printing, it’s better to take time to verify that it is indeed 3D printable, because this will save your time and print martial.

6. Optimizing an STL File For Best 3D Printing Performance

The 3D printer will print the object with same amount of coarse details which is already specified in the STL file.

By reducing triangles smaller and smaller, the approximation will be done better, which will yield better quality and smooth prints.

However, as we decrease the size of the triangles, the number of triangles that are required to cover the surface would increase more in numbers, which leads to larger STL file size, it would be difficult for 3d printer to handle it. Also, it is a daunting task and painful to share huge file size.

So it is very crucial to find the perfect balance between the file size and print quality.

7. Are There Any Alternatives To the STL File Format?

The STL file format is not only format for 3D printing, there are plenty of alternatives to STL files for 3D printing.

Another format PLY file is also used and were originally used to store 3D scanned objects.

However, as 3D printers continue to innovate and gain functionality, the new file format begin to surpass the capabilities of STL and other older file formats. 

3MF (3D Manufacturing Format) and AMF format (Additive Manufacturing) both aim to fully describe the 3D models such as internal information, color, materials, and texture.

As of now, both formats didn’t widespread compared to STL file format but as 3D printing technology continues to advance, they may become widely adopted.

8. Advantages and Disadvantages of Using STL File Format For 3D Printing

8.1 Advantages of Using STL File Format

The STL format is the most commonly used by professionals, amateurs but also machine makers and 3D printing services.

To be standard format file for 3D printing have its advantage

  • STL files are simple, light, and very easy to handle by software and machines.
  • Like we mentioned earlier, the STL file only contains the basic shape of the generated surfaces and their coordinates understood by the 3D printer, so the size is small. It is easier to email, download and share across with ease.
  • STL file format is universal and supported by nearly all 3D printers.
  • Most 3D printable models you can find on the internet are in the STL file format.
  • There are plenty of third-party software dealing with STL files, which is not the case with the other file formats.

8.2 Disadvantages of Using STL File Format:

Even if it is the most widely used format, the STL file format has limitations.

  • STL File only understands the external surface and shape of your model.
  • If you need to make a full-color 3D print,STL file cannot store detailed color and texture maps. In order to solve this,OBJ file format can be used
  • The gaps and overlaps of joining surfaces in the STL file model are not drawn correctly. These are known as non-manifold edges.

9. STL File Resources

I think right now you understand quite a bit about STL file format,let’s discuss about downloading 3D printable model, view, and repair the 3D STL file.

9.1 Downloading 3D Printing Model

Currently, there are tons of STL files (include free and paid) available online.

As long as you have one 3D printer, you can download them and print them out.

If you need 3D models to relate to your regular life stuff, read our dedicated article about this topic 65 Cool Things to 3D Print to Make Life Better in August 2020, we have organized the most cool and useful free 3D printable models for you and it is an updated list.

If you need Anime or video game characters 3D models, you can find them from many 3D models website, also find them from our website OXO3D 3D print files section.

We are specialized in creating Anime, Manga and video game character.

9.2 Opening and Viewing an STL File

Once you download model from online, before printing it, it is worth taking time to view your model, make sure the model is what you expected.

Sometimes, the 3D models that you downloaded is different to the images displayed in the website, especially when it is a free model.

And it takes time to print a model, so you need to check whether the 3D model is broken or missing some parts .

Fortunately, opening an STL file is not too complicated. There are several free STL file viewers for this purpose, which you can either use online or as a desktop application.

The Free STL file viewers List:

Software NameSystem
Autodesk ViewerOnline
STL Viewer for WordPressWordPress
GmshWindows, Linux
GLC-PlayerWindows, Mac, Linux
3D ViewerWindows
3D-Tool Free ViewerWindows
ADA 3DWindows
Open 3D Model ViewerWindows
STLViewWindows, Android
STLView 2.0Android
MeshLab for iOSiOS
18 Free STL file viewers software

9.3 Repair 3D STL File

Not all 3D files are printable. You need to repair them.

A typical STL file repair workflow contains the following steps:


The STL repair software’s wizard will attempt to fix all major errors, including holes, separate shells, and intersections.

Separating shells

A mesh consists of collections of connected triangles. It can contain multiple continuous surfaces that ideally are joined together while obsolete ones need removal.

Closing holes, bridging gaps

Some comprehensive STL repair programs allow different ways of hole filling, such as planar, tangent, ruled, or freeform.

Resolving overlaps and intersections

This typically requires recalculating entire portions of the mesh.

Filtering out

Filtering out double faces, double vertices, inverted normals, and sharp, narrow triangles.


Stitching open edges and remaining holes.

Manual repair

Manual repair by deleting and creating triangles.


Remeshing to optimize triangle count.


Exporting to the chosen mesh format.

Free Repair STL File Software
FreeCADan open-source and free to use CAD software. It offers many different tools for construction, like Drafts, Drawings, and Design features.
SketchUpa full-blown 3D modeling software that is now owned by architectural company Trimble Buildings. SketchUp is available as a commercial version called SketchUp Pro and as the free SketchUp Make edition.
Blendera great free program to either create models for printing, games, or video clips. It contains many useful tools for 3D printing.
MeshMixera free mesh editing program that you can download from AutoDesk’s website. It is very easy to edit STL files and also has a built-in slicer tool.
MeshLaba free open source program that allows you to view or merge, transform or repair STL, PLY, STL, OFF, OBJ, 3DS, and many other file types as well as point clouds.
3D Slasha free and easy to use 3D modeling software that lets you create models using a simple building-block concept similar to Minecraft.
SculptGLa free 3D sculpting tool. Unlike its professional cousins, like ZBrush, SculptGL includes only the basic tools necessary and allows you to give you a sense of the sculpting workflow.
7 Free Repair STL File Software


STL file is an important aspect in 3D printing since it serves as an interface between 3D model and 3D printer.

it is also important to know about STL files especially if you are planning to 3D print.

With this guide, you now have learned how STL file format works with a 3D printer, the difference between the STL file and other printing files.

If you found this article useful to you, please share it with your friends.

Do you have any other questions? let us know in the comments below.

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