Any ideas for making liquid soap really water-thin so it's suitable for foamer bottles?

Pretty much everything seems to increase viscosity
and foamer bottles require really water-thin soap so they work properly, otherwise they may break of clog from viscous soap.

The starting formula is really simple:
9% active SLES
3% active CAPB  (increases viscosity)
1-1.5% active Cocamide DEA/MEA/oleamide  (increases viscosity)
0.5-1% PEG-7 Glyceryl cocoate
citric acid to pH 5
no salt  (it would increase viscosity too)

when it arrives I'll try
0.25% HPMC to make them foam "tighter" and more stable (but likely it will increase viscosity too)

At this point I don't know what else to do
only diluting everything by at least 50% seems to work
and I can't switch SLES, CAPB because of projected costs and because we already have several drums of it.
Any ideas will be greatly appreciated.


  • You could use salt but go to the other side of the salt curve. There is a point in which salt starts to decrease viscosity.

    Fragrance also can reduce viscosity.

    Water soluble silicone might reduce the viscosity too.
  • You should observe an increase of viscosity when adding citric acid to get the pH 5. Try to keep the pH around 6.5-7 
  • As Perry suggested water soluble silicone copolyol will lower viscosity at 1-2%. DC surfactant 193.
  • "water soluble silicone" Silsense DW18
    Design of anti-aging creams, gels, and serums; shampoos; and therapeutic cosmetics. In-house label and box design capability.
  • you could try using carrageenan instead of HPMC; that makes formulas shear-thinning without substantially increasing the viscosity, and I know from experience that it works well in a foamer pack

    at my last place we used hexylene glycol to thin surfactant-based products, it's very effective at low levels
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • Does mixing everything at a higher than normal concentration, and then diluting with water to reach normal concentrations
    yields lower final viscosity, than mixing at normal concentrations from the beginning?

    My experiments suggest so.
    Maybe mixing concentrated ingredients creates some molecular attraction forces, that added water then weakens?

    Thanks to you all.
  • @Gunther I've never noticed that. Perhaps thixotropy is playing a role in there.

    Being a low price product I guess the cost is important, but something cheaper will reduce the foam too. Considering the cost are diols as bill suggested the best cost/benefit?. Other than the salt curve, it is effective, but horrible results. The remaining salt as it dries will most likely clog the valve.
  • Thanks guys I'll try that.
    I just ordered some HPMC to give it a try

    In this sample formulation from Evonik HPMC made foam clearly "tighter", as seen in the pics

    9.0 % Sodium Laureth Sulfate (Texapon NSO)
    3.0 % Cocamidopropyl Betaine (TEGO® Betain F 50)
    0.7 % Sodium Chloride
    2.0 % Polyglyceryl-3 Caprate (TEGOSOFT® PC 31)
    0.3 % Hydroxypropyl Methylcellulose (1.2 % TEGOCEL® fluid HPM 4000) resp. 0 % TEGOCEL® fluid HPM 4000 in control formulation

    I was about to try removing or sharply lowering CAPB to reduce viscosity
    but they took Cocamide/Oleamide off.

  • The CAPB, MEA or whatever, AND the citric acid are all increasing viscosity. Just use SLES, PEG-7 Glyceryl cocoate, preservative and fragrance; the pH will be around 6.5 probably.
    Design of anti-aging creams, gels, and serums; shampoos; and therapeutic cosmetics. In-house label and box design capability.
  • Update:
    I just realized I have Coco Betaine and not Cocamidopropyl Betaine
    They are not the same thing, and the former seems to increase viscosity more than the latter.

    Genagen thickening with salt

    I took of Cocamide DEA which was making it thicker and sticky

    So far, the following formula seems to remain water-thin:
    80% deionized water
    0.1% EDTA Na-4
    0.4% Sodium Benzoate (might add some extra Benzyl alcohol later, for preservative redundancy)
    1% SLS powder
    4.29% Texapon N70 (3% active SLES)
    10% Dehyton K (3% active CAPB)

    SLS:SLES  1:4 ratio for better foaming. 
    (although foam ain't that bubbly or "tight" as I'd wish, will try adding HPMC later)

    SLS+SLES Is just 4% to remain water-thin.
    Might try upping it to 4.5, 5% to improve foam.

    Active CAPB is a whoping 42% of total surfactants
    it was on purpose, to reduce irritation

    I might try adding some PEG-7 Glyceryl cocoate
    as it seems to lower viscosity a bit
    Too bad the chart has a logarithmic scale.
  • Besides PEG-7 GC I will try some tiny amounts of menthol and eucalyptol that seem to reduce viscosity.
    I wasn't able to find any studies on it, only anecdotal reports:
  • eucalyptol may separate. You should add tween 60 as well.
  • Update:

    PEG-7 GC (Cetiol HE) and Cocamide DEA leave a sticky feel that seems to remain for days.
    C-DEA further thickens it, so they're totally gone for good.

    So far,
    this formula seems to work great

    70% deionized water
    0.1% EDTA Na-4
    0.5% Sodium Benzoate
    1% SLS powder
    4.29% Texapon N70 (3% active SLES)
    10% Dehyton K (3% active CAPB)
    10% Bcare 2000 (about 5% active Decyl Glucoside)
    qs to 100% water
    qs to pH 5 (it takes about 0.5g citric acid to lower pH)

    Adding Decyl Glucoside adds great flash foam, taking advantage of the foamer bottle, while still keeping it water-thin.
  • You can probably get away with 0.3% benzoate.
    Design of anti-aging creams, gels, and serums; shampoos; and therapeutic cosmetics. In-house label and box design capability.
  • Thanks.
  • Sls powder is so irritating, why don't you avoid it? Use an already dissolved Sls instead  
  • Thanks for the suggestion @em88 a dust mark or preferably a woodworking respirator is definitely needed when working with SLS powder.
    I use the powder as I'm leaving room for natural watery extracts, on customer's request.

    It looks like the easiest way to drop sulfate formulations viscosity is to add a glucoside, it immediately kills viscosity.

  • Try adding about 5% SD Alcohol
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