If your objective is to create a prototype mug, you could 3D print the model, ideally without undercuts, then use the model as the "plug" for a silicone mold. If the mug has a handle, that would complicate things, but would still be possible. Once you have the mold, you could use any quality casting resin to generate another mug that isn't so sensitive to temperature. You'd want to sand away the layer lines or otherwise treat the 3D print (primer, glossy paint) before performing the casting, as silicone molding picks up every detail, even fingerprints! It adds another series of steps to the process, but you've referenced it as a prototype, not a production, justifying the extra work.