That's normal behaviour. It's called backface culling. Polygons have an order (defined by the order of the vertices in the edge definitions), that defines what's the front and what's the back. By default, the graphics hardware culls away the polygons that are backfacing and for most models, this is exactly what you want. In your case, not so much. You can toggle this behaviour be using setCulling(false); on the object. But keep in mind that the vertex normals that are used for lighting and such are also pointing away from the front side of the polygons, so your model's backside will be visible, but not lit.