Hi, film goes down by one stop when it is converted to redscale. This means that 200 speed film would be reduced to 100, so if using an auto camera, set the ISO to 400 to compensate for this.
What I have said here does not accomodate expiration dates for film, so if advice is needed on this too, just ask.
Sorry, but I don't know what you mean by 'hows does the number affect the material'. Be more specififc and might be easier to help you.
Hope this helped!