A TRI file isn’t built on one global format but is mostly used to store triangulated mesh data that computers can work with quickly, because 3D systems convert shapes to triangles as three points form a reliable flat surface, and the converted mesh is saved to avoid repeating the same heavy calculations, making the TRI file a derived format containing raw geometry such as vertex coordinates plus triangle index sets that keep file sizes smaller by storing only the essentials of the finished shape.

Apart from geometry, TRI files often incorporate surface-related data that assists with proper rendering, such as normal vectors for shading, UV coordinates for texture mapping, and occasionally optional features like vertex colors or material markers that differ by software, and since these files are binary and proprietary, one TRI file may be incompatible with another, meaning they are not meant for manual editing and instead operate as internal cache-like assets that the software can rebuild when required.

Typically, TRI files can be deleted safely after the program shuts down because the software can generate again the needed data later, causing only minor slowdowns on the next load, as these files act as temporary performance boosts rather than user-oriented formats, and since their structure is proprietary and tied to the program that made them, they cannot open like standard files, which is why no general TRI viewer exists and why different applications often embed completely different info within similarly named TRI files.

If the TRI file uses a text structure, simple tools like Notepad may reveal vertices or triangle definitions, though such cases are rare since TRI files are usually binary and built for quick loading, which causes a text editor to show random characters, not corruption, and because these files operate as intermediate representations, the software—not the user—typically loads them automatically, making direct opening outside the application’s workflow offer little insight.

There are times when multi-format viewers or identification tools can inspect a TRI file just enough to expose simple metadata or structural hints, which can help determine its purpose, but these tools rely on best-guess logic and may produce uneven results, and since TRI readability depends on the software that created it, the most reliable approach is to open it indirectly through that program, viewing TRI files as internal cache-like components rather than items for manual editing.