I'd like to get seals made to be used to make impressions in wax. Specifically, the ones here. I was looking at doing it through Shapeways or a similar site, using their fairly generically described "strong and flexible plastic". Is there a reason this wouldn't work well? Is there another material I should use? For some of the designs, it's showing concerns about wall thickness, which is as low as 0.33mm in some parts of the model. Is that something that I need to be considered given how small this will be and what I'll be using it for?

Thanks for any help!