Span-80 vs Tween-80: sorbitan oleate and polysorbate 80 compared

The short answer

Span-80 and Tween-80 are two nonionic surfactants built on the same sorbitan backbone. Span-80 is sorbitan oleate (CAS 1338-43-8); Tween-80 is polysorbate 80 (CAS 9005-65-6), which is essentially the ethoxylated version of that same sorbitan oleate. The one step - adding the polyethylene glycol chain - is what flips the molecule from oil-loving to water-loving, and that single change decides which way your emulsion can run.

What each one is

Span-80 (sorbitan oleate) is a lipophilic nonionic surfactant that works as a water-in-oil (W/O) emulsifier. It is an amber viscous grease at 25 degrees C and conforms to the Chinese chemical industry standard HG/T 3508, with a hydroxyl value of 190-220 mgKOH/g, saponification number 140-160 mgKOH/g, acid value <=8.0 mgKOH/g and water content <=1.5%.

Tween-80 (polysorbate 80) is the ethoxylated derivative of the same sorbitan oleate, a nonionic surfactant that works as an oil-in-water (O/W) emulsifier and solubilizer. It also presents as an amber viscous grease at 25 degrees C and conforms to HG/T 3510, with a hydroxyl value of 65-82 mgKOH/g, saponification number 43-55 mgKOH/g, acid value <=2 mgKOH/g and water content <=2%.

Span-80 vs Tween-80 at a glance

The one change that matters

Ethoxylation is the whole story. Span-80 is the sorbitan ester on its own - lipophilic, it prefers the oil phase and stabilises water droplets inside oil. Add the polyethylene glycol chain and you get Tween-80 - hydrophilic, it prefers the water phase and stabilises oil droplets inside water. Same starting backbone, opposite behaviour. This is why the two are often used together: a Span to set the W/O base and a Tween to fine-tune or invert the system.

How to choose between them

• Building a water-in-oil cream, lotion or industrial emulsion where the continuous phase is oil - start with Span-80.
• Building an oil-in-water system, or you need to solubilise an oily ingredient in water - Tween-80 is the natural fit.
• Working a food, pharmaceutical or personal-care system - confirm the applicable grade certificate, because food- or pharma-grade status is not part of the published specification data for either item.
• Matching an existing formula - check whether it calls for the sorbitan ester (Span) or the polysorbate (Tween); substituting one for the other changes the emulsion direction, not just the viscosity.

What is published, and what to confirm

For both items the identity (CAS) and specification block are cross-checked across client records - Span-80 across three consistent sources and Tween-80 across two. Neither item publishes food- or pharma-grade certification in its public specification; request the applicable grade certificate for regulated use. We recommend a lot-specific COA for incoming quality control. HLB is not stated in the published data for either, so selection here is made on emulsion direction and the documented spec values rather than a published HLB number.

Related reading

For the wider family context, see Span and Tween emulsifiers explained, and for choosing an anionic against a nonionic, nonionic vs anionic surfactants.