We currently offer two diaphragms that contain parylene:

Silicone Plus and EPDM Plus.

Parylene is a material that mechanically bonds itself to the base elastomer.  Parylene is similar to teflon in that it has very good chemical resistance and is a very slippery surface.

What this gives you is enhanced performance of the base elastomer.  In this case you will double the life of the diaphragm. Because we have to use a very thin application of Parylene we get enhanced chemical resistance, but not as good as Teflon. 
Probably the best feature of Parylene is that it eliminates the stickiness often encountered with EPDM.  This makes it very easy to remove the diaphragm from the valve.
Parylene is not a coating, it is a surface treatment that is applied by vapor deposition