# NEU Files: How to Open a Creo / Pro/ENGINEER Neutral File Online

A .neu file is a Pro/ENGINEER or Creo Neutral export, a text description of a part's faces and edges. Learn how to open one online, what is rebuilt and why its units need checking.

A `.neu` file is a Neutral file written by Pro/ENGINEER or Creo Parametric. It is plain text that starts with a `#UGC:2 NEUTRAL` header and lists a part's surfaces, edges and outline in a readable record tree. Older Pro/ENGINEER workflows used it to pass geometry between releases and to other programs, and it still turns up in archives and supplier packages next to `.prt` and `.asm` files.

You can open a NEU part in [the CADProps workspace](https://www.cadprops.com/workspace/index.md). The faces are rebuilt from the file and shown as a triangulated preview, so you can rotate the part, check its bounding box, measure point-to-point distances and export STL, OBJ, GLB, glTF, 3MF or mesh STEP after sign-in. The feature tree is not in the file, so there is nothing to edit.

## What is rebuilt from a NEU part

A Neutral part describes boundary geometry: each face names its carrier surface, and each edge names its curve and the faces it separates. CADProps rebuilds:

- planes, cylinders, cones and tori, in the coordinate frame stored for each surface;
- edges made of lines, circular arcs and splines stored as tangent-controlled segments;
- holes and inner loops, so a plate with bores keeps its bores.

The rebuilt faces are sewn together and, when they close up, treated as one body for display. A face whose surface type is not read, or whose boundary cannot be fitted back onto its surface, is left out instead of being guessed. The part is then marked incomplete and the warning tells you how many faces are missing.

The files we have tested come from older Pro/ENGINEER releases. Newer Creo exports can contain freeform or blended surfaces that are not read yet; those faces show as gaps.

## Check the units

The Neutral files we have seen do not state their length unit, so CADProps assumes millimetres and marks the units as assumed. Parts drawn in inches then read 25.4 times too small. Measure a feature whose size you know before you quote a dimension; [the scale factor guide](https://www.cadprops.com/guides/cad-model-wrong-scale-25-4/index.md) shows how to recognise 25.4 and other common factors. Area, volume and mass stay unavailable for NEU files.

## Assemblies and other limits

A Neutral assembly file only lists the parts it uses by name; it does not contain their geometry. CADProps does not fetch referenced files, so a reference-only assembly cannot be shown. Open the individual part files, or ask for a STEP export of the assembly.

Dimensions, annotations, colors and the feature history are not displayed. If you need exact surfaces, all face types or physical properties, export STEP from Creo: [what a STEP export keeps](https://www.cadprops.com/guides/step-export-no-feature-tree/index.md) explains what you lose either way. If you are not sure whether a `.prt` file came from Creo or NX, see [PRT file: NX or Creo](https://www.cadprops.com/guides/prt-file-nx-or-creo/index.md). The [format matrix](https://www.cadprops.com/supported-formats/index.md) lists every input and its limits.

## Related reading

- [STEP File Scale Wrong by 25.4? Fix Inch and mm Units](https://www.cadprops.com/guides/cad-model-wrong-scale-25-4/index.md)
- [IGES File (.igs, .iges): What It Is and How to Open It](https://www.cadprops.com/guides/iges-file-what-it-is-how-to-open/index.md)
- [Open a Rhino 3DM File Without Rhino](https://www.cadprops.com/guides/open-3dm-without-rhino/index.md)
- [Open CAD Files on Mac: STEP Viewers and Format Options](https://www.cadprops.com/guides/open-cad-files-on-mac/index.md)
- [F3D Files: How to Open a Fusion 360 Design Online Without Fusion](https://www.cadprops.com/guides/open-f3d-file-online/index.md)
- [NX or Creo PRT File? Identify the CAD Format](https://www.cadprops.com/guides/prt-file-nx-or-creo/index.md)
- [Why STEP Files Lose the SolidWorks Feature Tree](https://www.cadprops.com/guides/step-export-no-feature-tree/index.md)
- [What B-Rep Means in a STEP or IGES File](https://www.cadprops.com/guides/what-is-brep/index.md)

Original article: https://www.cadprops.com/guides/open-neu-file-online/

HTML page: https://www.cadprops.com/guides/open-neu-file-online/