3D printers require a specific input file type. Most use STL, short for stereolithography, which is an additive fabrication technology introduced by 3d Systems in the mid-1980s. While other AF technologies have emerged, the STL file format has remained the standard for most AF technologies, including 3D printing.
STL files are representations of surface geometry in a triangulated format. While some are finding ways to add color information to specific triangles within the STL structure and creating new file types that represent these colors, true STL files do not contain any color information. Color 3D Prints use different file formats, each has its strengths and weaknesses so these will be covered in another post. Over 90% of 3D prints use the .STL file format.
Many CAD applications can export geometry to the STL format. HOWEVER, be cautious when relying on the 'raw' export. Mistakes can exist within a STL file that will cause problems in 3D printing. All of the triangles in a STL file have a front and a back, or inside and outside. The front of the triangle is called a normal, and normals need to point the same way, outward. This is what defines an object's inside and outside. STL files exported directly from a CAD application tend to have inconsistencies in the normal directions. If the file is put into a 3D printer with inconsistent normals, there will be voids in the printed object.
It is necessary to check the quality of an STL file before 3D printing it with an STL viewer at minimum. Materialise's Magics software is the industry gold-standard in STL viewing and repair. There are other STL viewers available.
CADspan's resurfacing technology always outputs "good" STL files, meaning all normals will be oriented correctly (outward), and all geometry will be combined into one object. The resurfaced output file from CADspan describes a consistent, closed volume, where the inside and outside are clearly defined.