transparency in vray

hi :slight_smile: I am very new in vray.
I couldnt figure out which parameter defines transparency of an object in vray.
I examined the material settings, read the help files and even checked some of the water elements posted to the forums but I couldnot find out which setting makes a material transparent or not.
please help.

refraction color

white = 100% transparent

thanx :slight_smile: