Does anybody know if this treatment will work on untreated ripstop and still function properly?

Yes it will. Prewash the untreated ripstop in non-detergent soap and then put the treated item in the dryer for 60 min at medium heat. I have been unable to detect any difference in breathability and the repellency improves dramatically.

Thanks. I'll buy some ReviveX. I have an underquilt made from Jardine's kit. I want to treat the underside of the quilt for water repellancy, but still want breathability.