Superfatting Soap – An Explanation

I just got a fun question on superfatting for cold process soap over on TeachSoap and thought I’d expound a bit on superfatting cold process soap for everyone. First of all, if you haven’t seen the SoapQueen.TV video on superfatting, I have a handy dandy little explanation in there at minute 3:26 (completel with clay – yes, clay! to make my point).

Soapmaking is at its heart, a science. When we add colors and fragrance to the process, we turn the science into an art. Each oil has its own saponification value, or the amount of lye it takes to turn 1 gram of oil into 1 gram of soap. When we make cold process soap, it’s a mathematical formula that looks like this: (Oil Amount) x (SAP value) = Lye Amount needed. For a real example, it looks like this (10 oz. Olive Oil) x (.134) = .134 oz. lye. So, it takes 1.34 ounces of lye to turn 10 ounces of Olive Oil into soap. Using the exact amount of lye you need to make the exact amount of soap with nothing left over (no extra oils) is called a 0% superfat or a 0% lye discount.

Many soapmakers like to have some extra oils in their soap that are leftover and not bound to lye. Any extra oil left in the soap and not attacked by the lye is called a ‘superfat.’ The terms ‘superfat’ and ‘lye discount’ can be used interchangeably.


To figure out a superfat, you can do it a few different ways. My favorite is to let the lye calculator figure it out for you (!) or you can take the amount of lye that you are supposed to use and multiply it with the following equation (1 – % superfat you want). So, if you wanted to superfat your Olive Oil soap in the above example by 4%, you would do the following (.134 oz. lye) x (1 – .04) = .1286 oz. lye. Or you can do the rough ‘n’ easy way; for a one pound batch of soap, a 5% superfat works out roughly to .8 oz. of extra oils per pound of soap.

When I superfat my cold process soap I normally keep my superfat to 5% or less. I find that much more than that and my soaps are a wee bit soft, don’t lather quite as much as I like and also tend to go rancid more quickly. That said, superfat is a totally personal thing. I know some soapmakers that go up to 15% and swear by it.  I’d recommend experimenting a bit until you find the amount you love.  Soapmakers, I’d love to get your opinion on what your favorite superfatting range is. 


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  1. Sally says

    Loved the explanation and questions. i have learnt so much from you all tonight. Just wondering what INS stands for?

    • says

      Hi Sally!

      INS stand for Iodine Number Saponification and is the measure of the physical qualities of the spa based on the SAP and iodine values. Anne-Marie has actually tested INS soaps and the theory and she didn’t find that the INS numbers worked out for her. But it’s a total personal preference and many soapers do use and love them. =)

      ~Becky with Bramble Berry

  2. Rachael says

    Hi, and thanks for all this great information. It seems to me that superfatting with different oils would yield different results. For example, wouldn’t a surplus of Shea butter create a richer soap than adding more coconut oil? I don’t know if this is true, I am asking if anyone knows from experience if the same percent of superfatting with a different oil will tend to yield different moisturizing qualities.

    I was also wondering if, when superfatting at a higher percentage, does it help preserve the soap to add certain essential oils (i.e. ess. oils with antimicrobial, antifungal, etc properties) or other natural preservatives? Does anyone have experience with this? Thank you all! :)

  3. Mary says

    sorry that should have read (maybe with more coconut) you need a higher SUPERFAT blonde moment!!

  4. Mary says

    With reference to the comment you made about Kevin Dunn, could you please post a link to this? Also, some soapers are superfatting at 2% and some up to 15%, but does this affect the final pH? If there is no “free” lye left in the soap, I assume that the pH would be the same regardless of the superfat, as long as there is a superfat. Also, I think that if you make a very conditioning soap recipe with a low superfat or a less conditioning bar (maybe with more coconut) you need a higher pH. Personally, I always look at the INS end value. Commercial soap manufactures aim at a INS of 160. It is impossible to register an accurate pH with papers, you must use a professional meter.

    • Anne-Marie says

      There is no link to it. It was a verbal comment at a Soap Guild show maybe 5 (?) years ago. I’d love to have a link! But if you find something else out in your research, let me know. I always recommend a cure time of a minimum of 3-4 weeks even with that information.

      I haven’t tested it but I’m guessing that the 2% versus 15% superfat would probably affect pH by a small amount but not appreciable amount. But that’s just an educated guess.

      I’ve tested INS soaps and the theory and didn’t find that the INS numbers worked out (what the INS suggested, I didn’t like or find conditioning or any number of variables) but it’s a personal preference. There are a lot of soapers that use them and love them =)

  5. Amy says

    I superfat between 2% and 3%, but the soaps seem really rich anyway. I don't think I'd dare superfat any more lest they ended up feeling actively greasy.

  6. Anne-Marie says

    Hi Pamela,

    You can do the superfatting before the lye is added or at light trace. Though it would make logical sense that superfatting added at light trace is more nourishing because most of the lye has been neutralized because it's been paired with a fat molecule, Kevin Dunn from Caveman Chemistry proved that's not the case and that no matter when you add your fats, the pH of the final bar ends up the same (interesting, huh?!)

  7. Anne-Marie says

    Hi Claudia, Though we don't have a distributor in Mexico, you can always order through the website for smaller orders and we can ship to you. Anything over 250 pounds, we can put on a pallet and get to you even more cheaply though so email customer service for a shipping quote if you're buying in big bulk. =)

  8. Anne-Marie says

    I love love love everyone's comments! I've been noticing a higher superfat = higher soda ash for me so I've been at a 3% all summer but now that it's winter, am creeping up to the 4-5% range since I notice my skin needs a bit more TLC in the winter for sure.

    I love the idea of a 15% superfat for a facial bar!

  9. Duffin Soap Bakery says

    Thank you for the great post. I love what you explained. I use 5% superfat for my class and my own soap, too :)

  10. innerearthsoaps says

    Great explanation! I use 7% for most of my bars, makes 'em super mild, although in summer a little less to prevent rancidity.

  11. Ann Stoermer says

    I usually use %5 as well, as I love a nice thick lather and I also have issues with dry skin. I like the way you explained this – very nice.

  12. Pamela says

    Thank you so much for the explanation it is surely appreciated.
    I was taught 5% sf, and I have changed that up a bit 7% in drying winter here and 6% in dry hot summer.

    Does the video explain when to do your super fatting? Before trace with all oils, after lye is incorporated into the oils, or at light trace?

  13. LuAnn says

    I'm glad to see everyone's opinions on this, it's always interesting! Since I live in Idaho, it's VERY dry in the winter, so I actually use 8% superfat in the winter, and 5% in the summer. We have very dry, sensitive skin, so for our personal use, I superfat at 8-9%. And I love to use fresh goat's milk, that adds to the moisture, without taking away any more lather!

  14. Claudia E says

    Hi Anne-Marie. My name is Claudia from Monterrey, Mexico and your fan!! Congrats for you baby, I think she will be a little sweet girl.
    I´m a small business owner ( and I want to start making M&P soaps. I´ve seen all your videos about. Unfortunately, the colors and fragances I´ve found have poor quality. My question is if you have some dealers in Mexico whom I could buy your products?
    Thanks in advance.
    Claudia E.

  15. Jude, Aussie Soap Supplies says

    Great explanation AM. It often confuses people, and I still sometimes have difficulties explaining the term.

    I used 5 or 6% for many years, but lately have been dropping it to 4% to avoid DOS as our humidity here is increasing.

  16. Courtney R Beard says

    As someone with dry prone skin and little ones who need the extra moisture – I don't want my soaps too harsh. I've found doing a 7% superfat is my preference. Followed with a yummy homemade moisturizer of course. :)

  17. Cocobong Soaps says

    Thanks, Anne-Marie! I've been wanting to throw this question into the round for months. Shampoo soaps at 2%, Facial bars at 15% and all the rest between 8 and 9. I, too, love lather but can't compromise when it comes to conditioning. I find most soap (even handmade) too drying for my skin and it's my skin that has the last word :)

  18. Catherine Dreher - Owner says

    I superfat at 5%, though I have tried as high as 8% before.
    And I LOVE the Bramble Berry lye calculator. I use it all the time. I really like the new changes that let me type in the name of my soap and add notes, like what fragrances and colorants I used. And I like that I can now print it from a separate window. Before, I would input my information and then copy and paste it into a word document to avoid printing the entire web page. :)

  19. Splurge Sisters says

    What a great explanation. I used to superfat at 6% for a long time and then switched to my new favourite which is 7%.

  20. sironasprings says

    I like a 5% superfat, too! I'm a lather freak, so don't want too much excess oil inhibiting the bubbles.

    Nice explanation! I love the visual aids (colored clay)! :)

  21. Lori at The Nova Studio says

    Nice article Anne-Marie! I use 5% for my personal use & for most of our classes. It seems to be a good medium point between not enough and too much, if you know what I mean. :)