What Is the Difference Between STL Binary and STL ASCII?

Even though 3D printing is a hobby suitable for everyone regardless of technical expertise, there is no denying that technical expertise does come in handy on many occasions due to the complex nature of the process in terms of both software and hardware.

To be specific, troubleshooting and optimization are the two key areas that immediately come to mind where having a level of familiarity with the technical parts of the process, especially on the software side of things, can save a lot of time and effort spent, as general software knowledge often translates very well into 3D printing expertise.

In today’s article, our focus will be on a topic that is directly related to software knowledge, where we will be examining the differences between STL 3D model files with two distinct syntaxes, known as binary STL and ASCII STL, and finding out the advantages and disadvantages each of these syntaxes brings to the 3D printing process.

So, what are the differences between binary STL and ASCII STL files used in 3D printing?

The only difference between binary STL and ASCII STL files is their encoding, meaning that even though they both contain the same 3D model data that you can use for 3D printing without any issues, the way the data is stored in the file follows a different format and rules.

In the upcoming parts of the article, we will take a deeper look into the differences between binary and ASCII STL files, discuss the process of choosing between these two formats, find out how to identify whether an STL file is binary or ASCII, and finally, see if it is possible to convert ASCII to binary or vice versa.

What Is the Difference Between STL Binary and STL ASCII?

While both binary STL and ASCII STL files contain identical information about a 3D model and share the same extension, meaning they are practically the same type of file representing the same exact 3D model, their syntaxes are different, which separates the two at the end of the day.

In a nutshell, the difference between binary STL and ASCII STL is the difference in how the data is stored in the STL file and, as a result, how the computer reads the file and interprets it.

As the difference in encoding only impacts how the slicer reads the STL file and not the data that the file contains in the context of 3D printing, whether the STL file you have at hand is encoded in ASCII or binary will neither give you benefits nor cause problems.

On the other hand, for those who enjoy the technical bits, let’s take a quick look at the technical differences between ASCII and binary STL files.

The most glaring technical difference between binary STL and ASCII STL files is the file size, with binary STL files being a lot more optimized and taking up a lot less space than ASCII STL files as a result of this optimization.

Another technical difference between these two encoding types is that while binary STL files are not human-readable, it’s possible to open up any ASCII STL file in a text editor and read the code.

Finally, one last difference, even though it doesn’t have any effect in the context of 3D printing, is that ASCII STL files are not capable of storing color data, whereas the binary encoding makes it possible to keep the colors as well.

While rare, as any modern software that supports the importing of STL files should support both ASCII and binary encoding, it’s worth mentioning that the difference in encoding can prevent some (mostly legacy) software from opening the STL file, which is one factor that may affect you as the user.

How to Choose Between Binary STL and ASCII for STL Files?

While there isn’t much to separate binary and ASCII STL files, making a choice between the two can sometimes be necessary to ensure that the 3D printing process is conducted as optimally as possible and without problems.

In a nutshell, we recommend choosing between binary and ASCII STL files based on the software you will be importing the 3D model into, as the difference primarily concerns the interpretation of the file by the software rather than your experience during usage.

If the software you’re using supports both encoding types, which should be the case for all modern software that allows using STL files (such as the Cura slicer), we recommend going with binary STL as it’s newer and has a reduced file size.

Finally, while a rare scenario, it’s possible for some software to display buggy behavior with one encoding type and not the other in some cases, meaning that you can try using the encoding type you haven’t used before and see if it solves your problem.

How to Find Out Whether an STL File is Binary or ASCII?

Before moving forward with using the STL file that you have obtained, finding out whether it is a binary STL or an ASCII STL is an excellent idea to make sure that the file is compatible with the slicer software you will be using for the 3D printing process.

Every ASCII STL file starts with the word solid, followed by the name of the file, which is the primary identifier you can use to identify any ASCII STL file in a straightforward manner.

On the other hand, as binary is not a human-readable type of encoding, you will only see jumbled characters with no readable information if the STL file you have at hand is encoded in binary.

To see the contents of the STL file you have, you can quickly open it in the text editor of your choice and find out whether the string that signifies the STL file is encoded in ASCII exists or not. 

Is It Possible to Convert Binary STL Files to ASCII STL Files and Vice Versa?

Even though a binary STL file’s syntax is different from an ASCII STL file, they are essentially the same file type and convey the same information that the slicer software can utilize to understand the 3D model.

It’s entirely possible to convert binary STL files to ASCII STL files and vice versa automatically by using software that offers such functionality, as the data contained within files of both encoding types are identical for the 3D printing process.

As there is plenty of different software available (mostly free) that you can use to perform the conversion, you can feel free to use the one you choose.

Wrapping Up

While the differences between binary STL and ASCII STL are not obvious at all, especially if you haven’t opened files of both types in a text editor to inspect their contents, familiarizing yourself with the advantages and disadvantages of both syntaxes can definitely come in handy at times.

To quickly recap, ASCII and binary STL files are both capable of carrying the exact same information about the 3D model in the context of 3D printing, with the only difference being the encoding, which determines the way the data is stored within the file and does not affect the user experience in any way.

As the encoding primarily affects how the software interacts with the STL file and creates some other minor differences, such as file size and human readability, that don’t affect the 3D printing experience, it’s not something to worry about, for the most part, especially considering that modern software support both ASCII and binary encoding.

Happy printing!