58% nylon and 42% rayon.
This is NOT the sock yarn, also called Opal. This is a very slick, shiny woven yarn. Ball band says “Opal-Maxi” although something similar seems to have been produced by Lang under the names “Opal Color” and “Opal.”
As best I can tell, this yarn has been discontinued or at least renamed as just plain Opal.
The DK version is called Opal Lame.