Polyamide (SLS) can be treated with a sealant to fill small pores, thus making your model airtight and watertight. Of course, the final tightness will dependent on the initial level of pores, and the pressure of the water. This finish can be found when you upload a 3D file and select Polyamide (SLS) from the 'Materials' dropdown list and 'Waterproof White' from the 'Colors and Finishes' dropdown list.
