.STL

.STL is the most common file format when 3D printing. STL stands for STereolithography and .STL files consist of facet data. STL is a standard file format that can interface between most CAD software and 3D printers. .STL files contain only a single colour (an obvious limitation) and they are a triangular representation of a 3-dimensional object.

Despite the rudimentary data contained in an STL file, STL is the most popular file today. It’s supported by most 3D printers.

.OBJ

.OBJ is the second most common file format used in 3D printing. It is widely supported by 3D printers (such as the Formlabs 1+ and 2) and most software will export to .OBJ. This file is similar to .STL in that it contains 3D geometry information alone, such as vertex normals, geometric vertices, polygonal faces and texture coordinates.

OBJ builds on the STL file with multiple colours and material data. It also has improved model resolution support, so supports higher-quality prints.

.gcode

.gcode, otherwise known as .g or .gco, is the file extension for files containing G-code data. A .gcode file is created by a slicing program, which turns a CAD drawing into a string of code that a 3D printer can understand. You will come across this post-slicing file type a lot during your 3D printing efforts because it contains instructions for your 3D printer.

G-code contains instructions for your 3D printer. It’s a numerically controlled programming language generated by a slicing program.