Every STL is a promise made to a printer and kept to nobody else. It says: here are triangles, in millimetres by convention, and nothing else matters. When the source model is lost, when you bought a print file and want to change it, or when a scan needs to become a game asset, the trip back through OBJ in Blender is the standard move - provided you plan for the three things the STL cannot give back.
What survives, what does not
| Layer | STL | OBJ after conversion |
|---|---|---|
| Triangles | Yes | Yes, unchanged |
| Units | Millimetres by assumption | Same assumption - fix in Blender |
| UVs | No | Only what you unwrap yourself |
| Materials | No | Only what you author yourself |
| Part structure | Loose shells | Separable in Blender |
| Editing freedom | Full, once imported | Full |
The import pass
01 - Import and measure immediately. File, Import, STL. Ignore how it looks; read the dimensions. A tabletop figure should read 28 to 32 mm (0.028 to 0.032 in Blender metres), a desk prop in the centimetres, a scanned bust around half a metre. If the numbers are wrong by exactly 1000, a slicer wrote this file and you are the correction.
02 - Fix scale once, apply it, move on. Set the object scale or scene unit scale to make the dimensions real, apply the transform, and do not touch scale again. Every later problem - unwrapping, physics, export size - inherits whatever you leave here.
03 - Heal the mesh. Print files usually arrive watertight, which is wonderful, and filthy, which is not: merged vertices across thin walls, degenerate triangles, stray shells hiding inside the body. Merge by distance at a tiny threshold and run a quick cleanup pass before anything else.
04 - Separate what should move separately. Select the mesh and use separate by loose parts; a knight and his base and his spare sword become three objects you can actually work with, decimate and material independently.
Rebuilding what the STL never had
UVs. There are none, so enter Edit Mode and run a smart UV project - fast and slightly ugly, which is the correct trade for a print mesh. Refine islands by hand only where the camera will linger.
Materials. Assign per part, not per mesh: metal for the visor, leather for the strap, stone for the base. Painted textures need the UV work above; procedural materials need nothing and get you 80 percent of the look for a tenth of the effort.
Density. A resin-print mesh can carry a million triangles of noise it never needed. Decimate to the budget the destination asks for - a few hundred thousand for a render, a few tens of thousands for a game - and check the silhouette survives.
When this pipeline makes sense
Remixing a print you bought or downloaded; recovering a model whose source file is gone; turning a scan into a render or a game prop; scaling a miniature up for display, or down for a diorama. What does not make sense: converting STL to OBJ purely to print again. The printer was happy with the STL - let it stay in its lane, and leave the conversion for the moment the model needs to be edited.