The rules for WSF say that the thickness of walls should be greater than 0.7mm. I take it that this distance is generally measured from a polygon, through the model in the direction normal to the polygon, until it hits a polygon on the other side. This is how netfabb measures it, and how the measurements appear in the images Shapeways service send back from a rejected model. However, I think there are some edge cases when this measurement doesn't work. Here's an example: This is a triangular prism, and although the prism is quite large, you can find a "wall thickness" measurement that is under 0.7mm. Here are my questions: 1) Is this triangular prism printable? 2) If it is printable, how big does the triangular cross-section of a triangular prism need to be to be printable?