I did an online search as well, and even though I would have supposed it was made of alumina from the shape, the Dipper is not in the Alumina section of their website, but is with the Plugs. There is a small silicone plug video associated with the Dipper on the Tantus' website and its price is half that of the Pace.
So, since they also mention to use water-based lube, I'll go with silicone.