Red lines (unconnected edges) in Pepakura


I work with the combination of Blender and Pepakura for creating paper models. Sometimes it so happens that a seemingly perfect model in Blender has unconnected edges in Pepakura. These show up as red lines and result in a model where two faces are not connected although they should be.

There are several causes. One is that one or more vertices are duplicated, i.e. that two vertices are positioned at the same location. To fix this, go into Edit Mode, then press A to select all vertices, then press W and “Remove doubles”.

If that doesn’t help, in Edit Mode press ctrl+alt+shift+M. This selects non-manifold edges, i.e. edges where the model is open. Then press alt+M in order to merge the affected vertices.

If the problem still persists, you can recalculate the normals. Go into Edit Mode, select everything (press A), then press ctrl+N. The problem in this case is that each face of your model has an orientation. You can think of it as the “front” and “back” of the face. The so-called normal is a vector perpendicular to the plane of the face. Since the face has two sides, the normal can point in either of two directions. If a model consists of a contiguous surface where the normals of some faces are oriented differently than those of the other faces, Pepakura assumes that the surface isn’t actually contiguous (and rightly so).

In most cases, ctrl+N solves this problem automatically. However, there are some models which do not enclose a space completely, but which contain openings. In such a case, Blender may fail to orient all faces properly. You will see the problem in Pepakura by two sets of faces, one showing the texture (or face color) on the “outside”, and one showing it on the “inside” (double quotes, as technically there is no such thing as in and out for a model with openings). You can switch the orientation of the normals manually in Blender – here is a tutorial.

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  1. Combine,


    i found another way to Solve this, this should work with all Editors:

    Convert all Faces in faces not larger than 3 edges. For Blender: go in Edit mode, Selevt all faces, press ctrl + T


    1. admin,

      Good idea – depending on the actual problem with your model, this might very well work.

  2. James,

    hi, im working with pep, and im having that exact problem your talking about. actualy its showing the light gray inside color on the outside of some peies and the dark grey outside colors on the inside of those same peices. its odd.
    i tryed all your suggestions, and either im not doing it right, or the software has changed, im useing pepakura designer 3, i have a full paid copy.
    the only multiple select i can get going seems to be the drag box in the 2nd window on the select and move.
    could you please give me some more info?

    1. admin,

      Sorry, the instructions above are for Blender, not for Pepakura. The way I work is that I create / edit a model in Blender, then export it as a 3D Studio file, import it into Pepakura, and create the template there.

      Therefore, the steps described above only work in Blender. Unfortunately I am pretty sure there is no way of switching the normal of a face in Pepakura. Thus, you cannot fix the problem in Pepakura. You need some external editor.

      I have to warn you, though: If you have never worked in Blender before, the start is a bit rough. Once you get the hang of it, though, it’s a very nice piece of software.

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