Hi Danny, I'm not really familiar with UDM format, it seems to be a proprietary Moldflow format, and I'm not sure if there is any documentation available to describe it.

But I think it is not unusual for Finite Element Analysis programs to use a different kind of mesh structure where each mesh element is a little solid tetrahedron rather than a triangular surface facet.

So it is possible for there to be a different kind of mesh used for that kind of thing, I'm not sure if that is the case for your particular file or not though.

- Michael