A TRI file doesn’t follow one standard and is mostly created to store triangulated mesh data that computers can handle efficiently, with 3D tools converting complex shapes into triangles because three points provide a stable surface, and the resulting set is saved to avoid recalculating it every time, leaving the TRI file as a secondary format holding basic geometry like vertex positions and triangle index lists that keep the file small by keeping only the structure needed for the final model.

Beyond basic geometry, TRI files often hold surface data needed for proper display, including normal vectors for lighting, UV coordinates for texture mapping, and occasionally extras like vertex colors or material tags, though what appears depends on the software, and because the format is usually stored in a binary, non-human-readable structure, files from different tools may not match, meaning TRI files are generally not intended for manual editing and instead act as internal cache-style assets that can be rebuilt whenever required.

In normal workflows, TRI files may be deleted harmlessly after closing the software because the application can regenerate them whenever required, causing only slower loading next time, as they function like temporary optimized geometry caches rather than files intended for users, and since their binary structure is proprietary to each program, they cannot open like ordinary formats, leaving no universal viewer and allowing different applications to populate the .TRI extension with entirely different kinds of data.

On rare occasions, a TRI file stored as text can be opened with basic editors to show coordinates or triangle lists, but most TRI files are binary and tuned for fast processing, so text editors will display junk symbols due to their encoding, and since these files serve as intermediate geometry caches meant for the software’s internal use, they are normally accessed only by the program, leaving manual opening outside that environment nearly useless.

On occasion, broad file-viewing tools or file-identification programs can partially open a TRI file to show hints of structure or metadata, though their findings are based on guesswork rather than a true format specification, making results limited, and because TRI files are tightly bound to their originating application, the correct way to access their contents is through that software, while treating TRI files as background assets not designed for direct human use.