Waterproof and pressure sensor
That looks like a hydrophobic membrane. These have low surface energies and the force of attraction to the water is less than the surface tension of the water. Because of this the water is able to "ball-up".



Figure 1. Surface energy measurement. Source: Rame-Hart.

Surface energy is a problem in printing on plastic substrates, for example, as water-based inks won't wet. Solutions to the problem include corona treatment to increase the surface energy by knocking out some hydrogen atoms from the polymers and replacing them with oxygen atoms. This, in simple terms, provides more molecular hooks for the water.


  The strength of attraction between a material and a coating is determined by the relative surface energy/surface tension of the materials.  The higher the solid’s surface energy relative to the liquid’s surface tension, the greater the molecular attraction, this draws the paint, ink or adhesive closer for high bond strength.  The lower the solid’s surface energy relative to the liquid’s surface tension the weaker the attractive forces are and this will repel the coating. Source: Dyne Testing.


I would be afraid that thermal cycling will expel air from the enclosure and then, on contraction, suck water through the membrane. I would look for a sensor that could be mounted through the outside of the enclosure or read through a tube terminated on the casing. 



Figure 2. A pnuematic bulkhead fitting.



Figure 3. A bellows diaphragm. Source: AP Racing

On further thought, if your pressure variation is modest a bellows diaphragm would allow the pressure to equalise while maintaining weatherproofing. Put the bellows on the inside. The photo is some sort of car part but it might get you started on a search.