Trideceth-9 is a polyethylene glycol ether of Tridecyl Alcohol (q.v.). A synthetic ingredient used to keep products from separating. Often found in bath products like bubble baths, facial cleansing lotions, and hair shampoos and conditioners [Gottschalck 12th ed., pgs 2797]. Similar to Polyethylene glycols. The number indicates the thickness of the particular Trideceth [Winter 7th ed., pg 529].