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

What Is the HLB Scale? Origin and History

The Hydrophilic-Lipophilic Balance (HLB) concept was introduced by William C. Griffin of the Atlas Powder Company in 1949. Griffin recognised that every surfactant molecule has a characteristic balance between its water-loving (hydrophilic) portion and its oil-loving (lipophilic) portion. He proposed a numerical scale from 0 to 20 to quantify this balance, giving formulators a rational, predictive method for selecting .

Before Griffin's work, emulsifier selection was largely a matter of trial and error. A formulator might test dozens of surfactants before finding one that produced a stable emulsion. The HLB system transformed this process into a semi-quantitative science: if you know the required HLB of your oil phase and the HLB of your available surfactants, you can predict which surfactant—or which blend—will produce the most stable emulsion.

The HLB concept remains one of the most widely taught and applied tools in formulation science, used across personal care, agrochemicals, coatings, pharmaceuticals, and food technology. While more sophisticated methods have since been developed, the HLB scale endures because of its simplicity and practical utility.

The 0–20 Scale Explained: HLB Ranges and Applications

The HLB scale assigns a number between 0 and 20 to every . A value of 0 represents a completely lipophilic (oil-soluble) molecule, while a value of 20 represents a completely hydrophilic (water-soluble) molecule. The primary application of a surfactant depends on where it falls on this scale.

The table above reveals an important overlap: the O/W emulsifier range (8–18) encompasses the detergent (13–15) and solubiliser (15–18) ranges. In practice, a surfactant with HLB 15 can function as an O/W emulsifier, a detergent, or a solubiliser depending on concentration and formulation context. The HLB value tells you what the surfactant prefers to do, not what it is exclusively limited to.

Griffin's Calculation Method for Ethoxylated Nonionics

For ethoxylated nonionic surfactants—the largest class of nonionic surfactants used in industry—Griffin proposed a straightforward calculation:

HLB = 20 × (M_h / M)

Where:
M_h = molecular weight of the hydrophilic (polyoxyethylene) portion of the molecule
M = total molecular weight of the surfactant molecule

This formula is elegant in its simplicity. The fraction M_h/M represents the weight fraction of the hydrophilic part, and multiplying by 20 maps this fraction onto the 0–20 scale.

Example: Consider a lauryl alcohol ethoxylate with 7 moles of ethylene oxide (C₁₂EO₇).

• Molecular weight of lauryl alcohol (C₁₂H₂₅OH) = 186 g/mol
• Molecular weight of 7 EO units = 7 × 44 = 308 g/mol
• Total M = 186 + 308 = 494 g/mol
• M_h = 308 g/mol
• HLB = 20 × (308 / 494) = 12.5

This HLB of 12.5 places the surfactant squarely in the O/W emulsifier range, making it suitable for oil-in-water creams and lotions. As the number of EO units increases, the HLB rises; as it decreases, the HLB falls.

For polyhydric alcohol fatty acid esters (such as sorbitan esters), Griffin provided an alternative formula:

HLB = 20 × (1 − S / A)

Where S is the saponification number of the ester and A is the acid number of the fatty acid. This method is used for surfactants like the sorbitan ester and polysorbate series.

Davies' Group Contribution Method (1957)

In 1957, J. T. Davies proposed a more general approach that assigns a numerical value—called a group number—to each chemical group present in the surfactant molecule. The HLB is then calculated as:

HLB = 7 + Σ(hydrophilic group numbers) − Σ(lipophilic group numbers)

The Davies method is particularly valuable because it applies to all surfactant types—anionic, cationic, and nonionic—not just ethoxylates. It allows a formulator to estimate the HLB of a novel surfactant directly from its molecular structure without any physical measurements. However, the calculated values can differ from Griffin's values for the same molecule, so it is important to use one consistent method within a given project.

The Required HLB Concept: Matching Emulsifiers to the Oil Phase

One of the most powerful aspects of the HLB system is the concept of required HLB. Every oil, wax, or lipophilic ingredient has a characteristic HLB value at which it is most easily emulsified. This is called its "required HLB" for a given emulsion type (O/W or W/O).

The principle is simple: to make a stable emulsion, the HLB of the emulsifier system must match the required HLB of the oil phase. If the mismatch is more than about ±1 HLB unit, emulsion stability drops significantly.

When a formulation contains multiple oils, the required HLB of the oil phase is calculated as a weighted average based on the weight fraction of each oil. This is exactly analogous to the blend HLB calculation for emulsifiers (discussed below).

Calculating Blend HLB: The Weighted Average Method

In practice, a single surfactant rarely provides the exact HLB you need. Instead, formulators blend two (or more) —typically one with a low HLB and one with a high HLB—to achieve the target value. The blend HLB is calculated as a simple weighted average:

HLB_blend = (W_A × HLB_A + W_B × HLB_B) / (W_A + W_B)

Worked calculation: You need an emulsifier blend with HLB 10.5 to emulsify mineral oil. You have sorbitan monostearate (HLB 4.7) and Polysorbate 60 (HLB 14.9).

Let x = weight fraction of sorbitan monostearate. Then (1 − x) = weight fraction of Polysorbate 60.

• 10.5 = x × 4.7 + (1 − x) × 14.9
• 10.5 = 4.7x + 14.9 − 14.9x
• 10.5 − 14.9 = −10.2x
• −4.4 = −10.2x
• x = 0.431

Therefore, blend approximately 43.1% sorbitan monostearate and 56.9% Polysorbate 60 by weight to achieve HLB 10.5.

Verification: (0.431 × 4.7) + (0.569 × 14.9) = 2.03 + 8.48 = 10.51 ✓

Worked Example 1: O/W Hand Cream Formulation

Let us formulate an oil-in-water hand cream for personal care use. The oil phase consists of:

Step 1 — Calculate the required HLB of the oil-phase blend:

• Required HLB = (10/15 × 10.5) + (3/15 × 13.0) + (2/15 × 9.0)
• = (0.667 × 10.5) + (0.200 × 13.0) + (0.133 × 9.0)
• = 7.00 + 2.60 + 1.20
• = 10.80

Step 2 — Select emulsifiers and calculate blend ratio. Using sorbitan monostearate (HLB 4.7) and Polysorbate 60 (HLB 14.9):

• 10.80 = x × 4.7 + (1 − x) × 14.9
• 10.80 = 4.7x + 14.9 − 14.9x
• −4.1 = −10.2x
• x = 0.402

Blend: 40.2% sorbitan monostearate and 59.8% Polysorbate 60. If total emulsifier is 5% of the formulation (5 g per 100 g batch), use 2.01 g sorbitan monostearate and 2.99 g Polysorbate 60. Water phase makes up the remaining 80 g (plus preservatives, humectants, fragrance as needed).

Worked Example 2: Agrochemical Emulsifiable Concentrate (EC)

In agricultural chemistry, emulsifiable concentrates (ECs) are formulated by dissolving an active ingredient in a solvent (typically xylene or a proprietary aromatic solvent) and adding emulsifiers so that the concentrate self-emulsifies when diluted with water in the spray tank.

Consider a typical EC formulation:

The solvent phase is primarily xylene with a required HLB of 14.0. We select calcium dodecylbenzene sulfonate (HLB 3.5) as the lipophilic co-emulsifier and a with 12 EO (HLB 14.2) as the hydrophilic emulsifier.

Blend calculation:

• 14.0 = x × 3.5 + (1 − x) × 14.2
• 14.0 = 3.5x + 14.2 − 14.2x
• −0.2 = −10.7x
• x = 0.019

This result (only 1.9% of the calcium sulfonate) indicates that the required HLB is very close to the HLB of the hydrophilic emulsifier. In practice, the anionic co-emulsifier contributes electrostatic stabilisation beyond what HLB alone predicts. Experienced agrochemical formulators typically use 20–30% anionic co-emulsifier by weight of total emulsifier for combined steric + electrostatic stabilisation, adjusting by emulsion stability testing. A practical blend might be 2.5 g calcium dodecylbenzene sulfonate + 7.5 g nonylphenol ethoxylate 12 EO per 100 g concentrate.

Worked Example 3: Fragrance Solubilisation

Solubilisation is the process of forming a thermodynamically stable, optically clear solution of an oil in water using a surfactant above its critical micelle concentration (CMC). Fragrance oils typically require HLB values in the 15–18 range for successful solubilisation.

Consider solubilising 2% fragrance oil in water for a body spray. Fragrance oils are complex mixtures, but a typical required HLB is approximately 15.5.

Emulsifier selection: Polysorbate 20 (Polysorbate 20, HLB 16.7) is an excellent single-component solubiliser for this application. However, if a slightly lower HLB is needed for a specific fragrance blend, we can mix Polysorbate 20 (HLB 16.7) with Polysorbate 80 (HLB 15.0):

• 15.5 = x × 15.0 + (1 − x) × 16.7
• 15.5 = 15.0x + 16.7 − 16.7x
• −1.2 = −1.7x
• x = 0.706

Blend: 70.6% Polysorbate 80 and 29.4% Polysorbate 20. For 2% fragrance oil, typically 4–8% total surfactant is needed (a surfactant-to-oil ratio of 2:1 to 4:1), depending on the fragrance complexity. Using 6% total surfactant: 4.24 g Polysorbate 80 + 1.76 g Polysorbate 20 per 100 g, with 2 g fragrance oil and 91.94 g deionised water (plus preservative).

HLB for W/O Emulsions

Water-in-oil (W/O) emulsions require emulsifiers with low HLB values, typically in the 3–6 range. In a W/O emulsion, the continuous phase is oil and water droplets are dispersed within it. The emulsifier must preferentially partition into the oil phase, which is why lipophilic surfactants are required.

Classic W/O emulsifiers include:

• Sorbitan monooleate — HLB 4.3
• Sorbitan monostearate — HLB 4.7
• Glyceryl monostearate (GMS) — HLB 3.8
• Sorbitan tristearate — HLB 2.1
• Sorbitan trioleate — HLB 1.8

Many oils have different required HLB values for W/O versus O/W emulsions. For example, mineral oil has a required HLB of 10–11 for O/W but only 4 for W/O. Beeswax requires HLB 9 for O/W and 5 for W/O. The required HLB table above lists both values where data is available.

For enhanced W/O emulsion stability, it is common practice to blend a primary low-HLB emulsifier with a small proportion of a high-HLB to form a close-packed interfacial film. This technique, sometimes called the "emulsifier pair" approach, produces tighter packing at the oil-water interface and improved mechanical stability.

The Phase Inversion Temperature (PIT) Method

In the 1960s, Kaoru Shinoda and colleagues at Yokohama National University proposed an alternative to the HLB system known as the Phase Inversion Temperature (PIT) method. Shinoda observed that ethoxylated nonionic surfactants change their effective HLB with temperature: as temperature increases, hydrogen bonding between the polyoxyethylene chain and water weakens, making the surfactant progressively more lipophilic.

At a specific temperature—the PIT—the surfactant has equal affinity for both phases. At this point:

• Interfacial tension reaches a minimum
• The emulsion inverts (O/W → W/O or vice versa)
• Very fine droplets can be produced

The practical PIT emulsification technique involves heating the system to near the PIT (where ultra-fine droplets form), then rapidly cooling to 20–30 °C below the PIT to lock in the fine droplet size. This produces O/W emulsions with sub-micron droplets and excellent long-term stability—often superior to those produced by HLB matching alone.

The PIT method is particularly valuable for personal care emulsions and pharmaceutical creams, where fine particle size translates to improved skin feel and bioavailability. However, it is limited to ethoxylated nonionic surfactants and requires temperature control during manufacturing.

Limitations of the HLB System

While the HLB scale is an invaluable starting point, formulators should be aware of its limitations:

• Temperature dependence: The HLB system assigns a fixed number to each surfactant, but the effective HLB of ethoxylated nonionics decreases with increasing temperature. A surfactant that acts as an O/W emulsifier at 25 °C may become a W/O emulsifier at 60 °C. The PIT method addresses this limitation.
• Electrolyte effects: Dissolved salts can alter the hydration of the hydrophilic head group, effectively changing the surfactant's behaviour. High salt concentrations "salt out" ethoxylated nonionics, reducing their effective HLB. This is critical in agrochemical tank mixes with dissolved fertilisers and in industrial formulations with high ionic strength.
• pH sensitivity: While nonionic surfactants are relatively pH-insensitive, the HLB system does not account for pH effects on ionisable emulsifiers (such as fatty acid soaps), which can dramatically change their emulsifying behaviour across the pH range.
• Co-surfactant synergies: The HLB system treats surfactant blends as simple linear averages, but in reality can produce synergistic interactions—tighter interfacial packing, liquid crystalline phases, or lamellar structures—that dramatically improve emulsion stability beyond what HLB matching predicts.
• Does not predict droplet size or viscosity: Two emulsions with the same HLB match can have vastly different droplet sizes, rheology, and shelf life depending on processing conditions (shear rate, temperature, addition order).
• Limited to nonionic systems: Griffin's original method applies only to nonionic surfactants. While Davies' method extends to ionic surfactants, the concept of required HLB was developed and validated primarily with nonionic emulsifiers.

Despite these limitations, the HLB system remains the first tool most formulators reach for. It narrows the field of candidate emulsifiers from hundreds to a handful, after which systematic optimisation (varying HLB ±2 units, testing co-emulsifiers, adjusting concentration) produces the final stable formulation.

Practical Tips for Using the HLB System

• Always verify by experiment. The HLB system provides a starting point, not a final answer. Prepare a series of emulsions spanning ±2 HLB units around the predicted optimum and evaluate stability at 24 hours, 1 week, and 4 weeks.
• Use emulsifier pairs. A blend of low-HLB and high-HLB surfactants almost always outperforms a single surfactant of the same HLB value. The pair produces closer packing at the interface and often forms stabilising lamellar or liquid crystalline structures.
• Total emulsifier concentration matters. Too little emulsifier gives insufficient coverage; too much wastes material and can cause unwanted foaming or irritation. Typical levels are 2–8% of the total formulation for cosmetic emulsions and 5–15% for agrochemical ECs.
• Consider the phase volume ratio. For very high internal-phase emulsions (above 60% dispersed phase), the standard HLB approach may need adjustment, and additional rheological modifiers or polymeric stabilisers may be required.
• Account for temperature. If the emulsion will be stored or used at elevated temperatures, consider the PIT of your surfactant system and ensure the storage temperature is well below (for O/W) or well above (for W/O) the PIT.

HLB Values of Common Emulsifiers

Conclusion

The HLB scale, despite being over seven decades old, remains a cornerstone of emulsion formulation science. Griffin's elegant 0–20 scale and the concept of required HLB give formulators a rational starting point for emulsifier selection. Davies' group contribution method extends the framework to all surfactant types. And when combined with modern refinements like the PIT method and an understanding of , the HLB system becomes a powerful predictive tool.

At Esteem Industries, we offer a comprehensive portfolio of , alkoxylates, ester-based emulsifiers, and spanning HLB values from below 2 to above 18. Our technical team can help you identify the optimal emulsifier system for your specific formulation challenge—whether it is a stable cosmetic emulsion, a self-emulsifying agrochemical concentrate, or a high-performance industrial coating.