Hygroscopic=water absorbing, think sucking moisture from the air.
Polyglycol DOT 3 & 4 brake fluids and silica gel are hygroscopic.
Hydrophilic is water loving, meaning it will hold on to water if exposed to
liquid water.  Think gelatin, or our body tissues.   Hydrophobic repels
water, think wax or silicone water proofing.

I once tried hydrophobic DOT 5 silicone brake fluid in my old MGBs thinking
it was the permanent solution, but I learned quickly that moisture condensed
on the inside of the metal reservoir used in those days and just sat on the
bottom and eventually worked its way into the master cylinder turning
everything into a rusty mess.  So much for that idea. I'm now on a two year
flush cycle on all my cars now using a DIY pressure bleeder from Motive
Products.

Stuart, a chemist in a previous life

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Robert Stevens
Sent: Wednesday, June 20, 2012 6:11 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: source for rebuilt ATE calipers?

> but then generally, conventional brake fluid is hydroscopic I think is
> the word..

Not that it really matters, but I think you are talking about hydrophilic,
water-attracting molecules. Greek for love of water. Which ain't no kinda
love for our brake/clutch systems. ;-)

bob