The HLB Scale: A Formulator's Guide to Emulsifier Selection

What is HLB?

HLB is a relative scale from 0 (fully lipophilic) to 20 (fully hydrophilic). Nonionic surfactants with long ethylene oxide chains sit at the high end; sorbitan monoesters with little or no EO sit at the low end. The number represents the balance between the hydrophilic and lipophilic portions of the molecule and correlates with the type of emulsion a surfactant will favour.

Griffin's original method calculates HLB for ethoxylated nonionics from molecular weight ratios. In practice, formulators use published HLB values for commercial grades and blend two or more emulsifiers to achieve a target system HLB.

Required HLB: matching emulsifiers to the oil phase

Each oil, wax, or lipophilic active has a required HLB — the system HLB at which it is most easily emulsified in an O/W system. When the emulsifier system HLB matches the required HLB of the oil phase, emulsions form more readily and tend to be more stable. Required HLB is determined experimentally and published in formulation handbooks; values below are representative guides.

Calculating blend HLB

When blending two or more emulsifiers, system HLB is the weighted average:

System HLB = (fraction A × HLB A) + (fraction B × HLB B) + …

Example: 70% Polysorbate 60 (HLB 14.9) + 30% Sorbitan stearate (HLB 4.7) gives 0.7 × 14.9 + 0.3 × 4.7 = 10.4 + 1.4 = 11.8. This is close to the required HLB of mineral oil (10–11) and suitable for an O/W cream containing mineral oil in the oil phase.

Worked example 1: O/W hand cream

Formula target: 15% oil phase (cetyl alcohol + mineral oil), O/W emulsion, stable at 40°C storage.

Step 1: Calculate weighted required HLB of oil phase. Mineral oil (required HLB ~10.5) at 10% plus cetyl alcohol (required HLB ~15) at 5% gives weighted required HLB ≈ 11.

Step 2: Blend emulsifiers to system HLB 11 — e.g. 70% Polysorbate 60 (HLB 14.9) + 30% Sorbitan stearate (HLB 4.7) → calculated system HLB ≈ 11.8.

Step 3: Use 4–5% total emulsifier on formula weight. Heat oil and water phases separately to 75°C, combine with homogenization, and cool with gentle stirring.

Step 4: Adjust viscosity with 0.1–0.3% electrolyte or 0.5% xanthan gum if needed. Run 40°C / 75% RH stability for 4 weeks minimum.

Worked example 2: Agrochemical EC dilution

An emulsifiable concentrate containing 50% actives in aromatic solvent must disperse into hard water at 1:500 dilution without creaming or oil separation.

• Target emulsifier system HLB 10–12 for the solvent/actives blend.
• Blend calcium dodecylbenzene sulfonate (hydrotrope/wetting aid) with C9–C11 alcohol ethoxylate (5 EO) at approximately 1:1 ratio.
• Total emulsifier package typically 8–15% of the EC formula.
• Test CIPAC 36.1 dilution stability at 0°C, 20°C, and 54°C before registration.

See also our emulsifiable concentrates guide for EC formulation principles.

Worked example 3: Fragrance solubilization

To clear-solubilize 1% perfume oil in an aqueous toner without cloudiness:

• Use Polysorbate 20 (HLB ~16.7) at a minimum 3:1 surfactant-to-oil ratio — i.e. 3% PS 20 for 1% fragrance.
• Pre-mix fragrance with polysorbate before adding to water.
• Increase ratio to 4:1 or 5:1 for difficult terpene-rich or resinous oils.
• If clarity is marginal, add 0.5–1% ethanol as co-solvent.

HLB for W/O emulsions

W/O emulsions require low-HLB emulsifiers in the 3–6 range. A water-in-mineral-oil formulation might use sorbitan oleate (HLB ~4.3) or glycerol monooleate (HLB ~3.8) as the primary emulsifier, possibly with a low-EO fatty alcohol ethoxylate as co-emulsifier. The required HLB concept still applies but targets the W/O side of the scale.

History and development of the HLB concept

The HLB system was introduced in 1949 by William C. Griffin, a chemist working at Atlas Powder Company (later absorbed into ICI Americas), who needed a systematic way to rank the growing number of sorbitan-ester and polysorbate emulsifiers the company was commercializing. Griffin's original paper, published in the Journal of the Society of Cosmetic Chemists, proposed a simple arithmetic method: for fatty acid esters, HLB = 20 × (1 − S/A), where S is the saponification number of the ester and A is the acid number of the fatty acid. For surfactants where saponification is not straightforward, Griffin offered an alternative based on the weight percentage of the hydrophilic portion of the molecule divided by five, capping the practical scale at 20.

In 1957, Australian chemist Norman Davies extended the concept with a group-contribution method that assigns numerical values to specific chemical groups — sulfate, carboxylate, ether oxygen, hydroxyl — and sums them to estimate HLB directly from molecular structure. The Davies method was a significant advance because it could be applied to ionic surfactants that Griffin's original saponification approach could not handle well, broadening HLB's usefulness beyond the nonionic esters it was originally designed for.

A related but distinct approach is the phase inversion temperature (PIT) method developed by Kozo Shinoda in the 1960s. Rather than assigning a fixed number to a surfactant, PIT identifies the temperature at which an O/W emulsion inverts to W/O as the nonionic emulsifier's hydrophilicity decreases with rising temperature. PIT-based formulation is widely used alongside HLB in cosmetic and industrial emulsion design, particularly for systems stabilized by ethoxylated nonionics whose solubility is strongly temperature-dependent. Modern formulators often combine HLB for initial emulsifier screening with PIT or direct stability testing for final optimization, since no single number fully captures real-world emulsion behaviour.

Limitations and practical tips

HLB is a starting point, not a guarantee of emulsion stability. Real-world behaviour is also affected by:

• Temperature — cloud point and emulsion viscosity change with temperature; a stable room-temperature emulsion may separate at 40°C.
• Electrolytes — salts compress the electrical double layer and can break O/W emulsions or invert them.
• pH — ionic emulsifiers change charge state; ester-based emulsifiers may hydrolyse at extreme pH.
• Co-surfactants and thickeners — fatty alcohols, waxes, and polymers build viscosity and gel network stability beyond what HLB alone predicts.
• Phase volume ratio — high internal phase emulsions need more emulsifier than dilute systems.

HLB troubleshooting in the lab

Treat a failed emulsion as a diagnosis, not a reason to abandon HLB. Creaming with intact droplets usually means coarse size or low continuous-phase viscosity — homogenize more or add a thickener before you swing blend HLB by three units. Free oil is coalescence: retune toward the oil's required HLB, check that esters were not hydrolysed, and confirm both phases were at the same temperature when combined. Grain on cool-down is often unmelted stearate or fatty alcohol, not an HLB miss.

Mixed-oil required HLB and experimental ladders

Required HLB of a mixed oil phase is the weighted average of the components, but polarity modifiers shift the experimental value by one or more HLB units. Ethanol, isopropyl myristate, volatile silicone, and high-melting waxes are the usual culprits: a mineral-oil cream that needed HLB 10.5 can need 12 once a polar ester is added, or 9 once beeswax dominates. Always confirm with a small ladder of blend HLB (for example 9, 10, 11, 12) rather than a single calculated number, using the same process temperature and homogenization on each trial.

Bancroft's rule still helps: the phase in which the emulsifier is more soluble tends to become continuous, so high-HLB favours O/W and low-HLB favours W/O. It fails when phase volume is extreme, when a polymeric thickener locks morphology, or when an ethoxylated nonionic crosses its phase inversion temperature. Ionic co-emulsifiers sit outside Griffin's original saponification formula; treat their published HLB as approximate and rely on salt, hardness, and freeze–thaw tests. PIT measurement on the actual oil blend is the best complement to Griffin HLB when the emulsifier is a fatty alcohol ethoxylate whose hydration depends strongly on temperature.

Always validate with accelerated stability testing and application-specific performance tests. For complex systems, Venus technical support can recommend fatty alcohol ethoxylates, polysorbates, and custom emulsifier blends. Read surfactant vs emulsifier for context on when HLB applies. Contact Venus for samples and HLB matching support.