Sorbitan fatty acid esters, commonly known by the trade name Span, are a family of non-ionic emulsifiers ranging from amber liquids to waxy solids. Each grade has a different balance between oil and water affinity, which determines how it behaves in an emulsion and where it performs best. This guide covers what Span is, how the main grades compare, where they are typically used, and how to choose between them.
Span products are formed by esterifying sorbitol with fatty acids, producing non-ionic surfactants that remain stable across a wide pH range and are compatible with most other ingredients in a formulation.
The single most useful number for working with any Span grade is its HLB (Hydrophilic-Lipophilic Balance). Lower HLB values indicate a more oil-loving character, suited to water-in-oil (W/O) emulsions, while higher HLB values shift toward greater water compatibility. Across the Span series, HLB decreases steadily from S-20 (8.6) down to S-85 (1.8), meaning the series spans from the most water-compatible grade to the most strongly oil-compatible one.
The table below summarizes the key specification parameters for the five common grades.
| Grade | Appearance (25°C) | HLB | Melting Point (°C) | Acid Value (mgKOH/g) |
|---|---|---|---|---|
| S-20 | Amber viscous liquid | 8.6 | Liquid at 25°C | ≤ 8 |
| S-40 | Yellowish waxy solid | 6.7 | 45–47 | ≤ 8 |
| S-60 | Yellowish waxy solid | 4.7 | 52–54 | ≤ 8 |
| S-80 | Amber viscous oil | 4.3 | Liquid at 25°C | ≤ 10 |
| S-85 | Yellow oily liquid | 1.8 | Liquid at 25°C | ≤ 15 |
All grades carry a moisture content of 1.5% or below, with saponification values generally in the 135–185 mgKOH/g range depending on grade. Beyond the numbers, each grade has a characteristic profile:
S-20, with the highest HLB in the series, is soluble in oils and organic solvents and disperses in water as a semi-emulsion. It functions as a W/O emulsifier, stabilizer, plasticizer, and lubricant, and is also used as a textile softener and antistatic finishing agent.
S-40 is a waxy solid that dissolves in oils and organic solvents and disperses in hot water. It is commonly used as an emulsifier and dispersant in food and cosmetic formulations, as a stabilizer in emulsion polymerization, and as a dispersant in printing inks and textile coatings.
S-60 is insoluble in cold water but disperses in hot water, offering strong emulsification, dispersion, and lubrication along with good stabilizing and defoaming behavior. It is widely used in food applications such as beverages, confectionery, ice cream, baked goods, and chocolate, and as an antistatic and softening agent for acrylic fibers.
S-80 is insoluble in water but dissolves readily in hot oils and organic solvents, making it a high-grade lipophilic emulsifier for W/O systems, oil-based drilling fluids, coatings dispersion, and pigment stabilization. It also serves as a co-solvent in petroleum products and a rust inhibitor in anti-rust oils.
S-85, with the lowest HLB in the series, is the most strongly oil-compatible grade, slightly soluble in solvents such as isopropanol and tetrachloroethylene. It is mainly used in pharmaceutical, cosmetic, textile, coating, and petroleum applications as an emulsifier, thickener, and rust inhibitor.
Across personal care and cosmetics, Span grades act as W/O emulsifiers and stabilizers in creams and lotions, often paired with Tween-series emulsifiers to balance overall HLB. In food production, grades such as S-60 serve as emulsifiers and stabilizers in beverages, confectionery, ice cream, baked goods, margarine, and chocolate. In pharmaceuticals, Span esters contribute to the stability and texture of emulsion-based creams and formulations.
A distinct application area is anti-fog film additives, where Span grades are incorporated into PVC, polyolefin, and EVA films to provide initial and low-temperature anti-fog performance, typically at dosages of around 1–1.8% in PVC film and 0.5–1% in EVA film, depending on grade.
Beyond these areas, Span esters are used industrially as textile softeners and antistatic agents, dispersants in printing inks and coatings, emulsifiers in oil drilling fluids, wetting agents and emulsifiers in pesticide formulations, stabilizers in pigment production, and rust inhibitors in anti-rust oils.
Choosing between Span grades comes down primarily to HLB and the desired emulsion type. Higher-HLB grades such as S-20 partition more readily toward the water phase and suit systems with lower oil content or where rapid dispersion is needed. Lower-HLB grades such as S-80 and S-85 partition more strongly toward the oil phase and suit high-oil-content systems or W/O emulsions requiring greater stability.
In practice, Span esters are frequently combined with Tween-series polysorbates — their more hydrophilic, ethoxylated counterparts — to reach a target overall HLB. By blending a low-HLB Span with a high-HLB Tween in different ratios, formulators can fine-tune the system to match a specific oil phase, often achieving more stable emulsions than either emulsifier could provide alone. Physical form, melting point, and solubility behavior should also be considered, since these affect handling and incorporation into a formulation.
Span products are non-toxic and non-flammable, and are classified and transported as non-dangerous goods under general chemical handling guidelines. They are typically supplied in 200 kg iron or plastic drums, 50 kg plastic drums, IBC totes, flexitanks, or tank cars depending on order volume, and should be stored in a dry, ventilated location with a shelf life of approximately two years under proper conditions.
