While it doesn't appear on the API documentation site, the Web Service Description indicates that for the data type SWModel used for the submitModel function, there is a parameter "materials": Code: <xsd:element name="materials" type="xsd:array" nillable="1"/> I tried using the materials parameter for a PHP batch upload script I am using to upload tens of models in one operation. The script works fine when not using the materials field. I have a small set of test models that pass the test when uploaded through the API. As soon as I specify the materials parameter, however, I start getting this error email: It is unclear to me why this error appears. The model uploads and validates just fine when not specifying materials. Maybe the materials parameter is not working correctly? I realize that this is an undocumented feature and therefore it would be fair to say that I cannot possibly expect it to work. But since the parameter is already there in code and because others have asked for it here in the forums, I figured I'd flag this up. It would be extremely helpful to me (and probably others) if you could make the materials parameter work. If I could specify the available materials for the model through the API, it would save me hours of repetitive clicking in the web interface.