Maryann , I think it is the humidity that causes the clumps. I had some foot soak that I had mixed up ( salts, baking soda, some powdered milk and eo's etc.) I covered it with glad press and seal and put it in a cabinet in the kitchen until I could package it. A few days later it had quite a few hard small pebbles that looked like it was mostly the baking soda and salts that combined with the moisture from the eo had in fact clumped up. It gets extremely humid here in FL so my suggestion would be to make sure and seal it real well and don't add your liquid ingredients until you are ready to package it. I use the disposable glad containers ( Tupperware would be better cause you could burp it lol ) Also after mixing in the liquid try sifting it since I think that helps incorporate all the ingredients. Now that I have blathered on, to answer your question I don't know of a product specifically made to inhibit clumping. Oh yeah, one more thing, if you have "Natrasorb Bath" this is an excellent way to add your oils and fo. It keeps the moisture out of the mix and when it hits the water it releases the fragrance and oils. Sorry for the book:cheesy2: Hope the info helps.