Dipropylene glycol — DPG for short — is one of those ingredients that shows up across a surprisingly wide range of industries without most people knowing much about it. It is in the fragrance oil you use to fill a reed diffuser, in the polyurethane foam in your furniture, in industrial cleaning formulations, and in personal care products. The same compound, doing different jobs depending on the context.
This guide covers what DPG actually is, what makes it useful, how it is graded for different applications, and where it fits compared to propylene glycol. No unnecessary depth — just what you need to understand the material and make informed decisions about it.
What Is Dipropylene Glycol?
DPG is produced as a byproduct during the manufacture of propylene glycol (PG). When propylene oxide is hydrated to make PG, some of the PG molecules react further with additional propylene oxide to form DPG — essentially two PG units linked by an ether bond. This makes DPG a dimer of PG, with roughly double the molecular weight and significantly different physical properties.
One important detail: DPG is not a single compound. It is a mixture of three structural isomers — 2,2′-oxydipropanol (the major isomer), 1,1′-oxydipropanol, and 1,2′-oxydipropanol. The ratio of these isomers varies by production process and affects the odor and solvency of the final product. This is why fragrance-grade DPG, which is refined to minimize odor-contributing isomers, is specified separately from industrial-grade DPG.
- INCI name: Dipropylene Glycol
- CAS number: 25265-71-8 (mixed isomers); 110-98-5 (pure 2,2′-isomer)
- Chemical formula: C₆H₁₄O₃
- Molecular weight: 134.17 g/mol
- Appearance: Clear, colorless liquid
- Odor: Essentially odorless (fragrance grade); faint odor (industrial grade)
Key Properties
| Property | Value |
|---|---|
| Boiling point | 229–232°C |
| Flash point | ~124°C (closed cup) |
| Density (20°C) | ~1.027 g/cm³ |
| Dynamic viscosity (20°C) | ~84 mPa·s |
| Vapor pressure (20°C) | <1 Pa (very low — slow evaporation) |
| Pour point | –47°C |
| Water solubility | Fully miscible |
| Shelf life | 24 months (sealed); use within 12 months after opening |
The two properties that define most of DPG’s commercial value are its very low vapor pressure and its near-zero odor (in fragrance grade). Low vapor pressure means it evaporates slowly — which is exactly what you want in a fragrance carrier, a reed diffuser base, or a high-temperature industrial fluid. Near-zero odor means it does not interfere with the scent of whatever it is carrying.
Grades and What They Mean
DPG is commercially available in two main grades, and the distinction matters for sourcing:
Fragrance Grade (Low-Odor Grade)
Fragrance-grade DPG is refined to maximize the proportion of the low-odor 2,2′-isomer and minimize the isomers that contribute a faint but perceptible odor. Purity is typically ≥99.5%. This is the grade required for perfumery, personal care, and any application where the DPG will be in close contact with a scent composition. Using industrial-grade DPG in a fine fragrance formulation risks introducing a background odor that interferes with the scent profile.
Industrial Grade
Industrial-grade DPG has a broader isomer mix and a faint but detectable odor. Purity is typically ≥98.0%. It is suitable for polyurethane production, resin manufacturing, functional fluids, and other industrial applications where odor is not a concern. It is generally less expensive than fragrance grade.
When sourcing DPG, always specify the grade. A supplier quoting “DPG” without grade specification may be offering industrial grade, which is not appropriate for fragrance or personal care applications.
Applications
Fragrance and Perfumery
This is DPG’s largest personal care application and the one it is most associated with. Fragrance-grade DPG is the standard carrier and diluent for fragrance oils, aroma chemicals, and essential oil blends. Perfumers dilute concentrated fragrance materials in DPG to create workable concentrations for blending and testing. It dissolves most fragrance components effectively, does not contribute its own scent, and its slow evaporation rate helps extend the longevity of the fragrance on skin or in a diffuser.
In reed diffusers, DPG is typically used at 60–80% of the formulation, with fragrance oil making up the remainder. Its low viscosity and excellent capillary action allow it to wick up rattan reeds efficiently, releasing fragrance gradually over weeks. In roll-on perfumes and body oils, it serves as the carrier base, providing a smooth, non-greasy application.
Personal Care and Cosmetics
Beyond fragrance, DPG appears in personal care formulations as a mild humectant, co-solvent, and texture modifier. It is less hygroscopic than propylene glycol or glycerin, which means it attracts and holds less moisture — but this also means it feels lighter and less sticky on skin. At 3–10% in a leave-on product, it provides mild hydration and helps dissolve water-shy active ingredients that would otherwise be difficult to incorporate.
It is also used as a coupling solvent — helping oil-soluble and water-soluble ingredients coexist in a single phase without requiring additional surfactant-based solubilizers. This is useful in toners, essences, and lightweight serums where a clean, non-emulsified texture is desired.
Polyurethane Production
Industrially, one of DPG’s most significant uses is as a reactive diol in polyurethane (PU) chemistry. When DPG reacts with diisocyanates (MDI or TDI), its two hydroxyl groups form urethane linkages that become part of the polymer backbone. The molecular weight and structure of DPG influence the flexibility and hardness of the resulting PU product — it is used in flexible foam formulations, coatings, adhesives, and sealants. This is a high-volume industrial application that accounts for a substantial portion of global DPG consumption.
Unsaturated Polyester Resins
DPG is used as a glycol component in unsaturated polyester resin (UPR) production, where it contributes flexibility and improved impact resistance to the cured resin. UPRs are used in fiberglass composites, marine applications, construction materials, and automotive parts. The choice of glycol in UPR formulation affects the resin’s mechanical properties, and DPG is selected when a balance of flexibility and processability is needed.
Functional Fluids and Industrial Applications
DPG’s low freezing point (–47°C pour point), thermal stability, and low volatility make it suitable for use in heat transfer fluids, de-icing formulations, and hydraulic fluids. It is also used as a solvent in printing inks and paints, where its slow evaporation rate helps control drying speed and film formation. In industrial cleaning, it functions as a co-solvent in formulations where a slower-evaporating, less volatile alternative to propylene glycol is needed.
DPG vs Propylene Glycol: When to Use Which
DPG and PG are related but not interchangeable. The choice between them comes down to a few practical factors:
| Factor | Choose PG | Choose DPG |
|---|---|---|
| Evaporation rate needed | Faster evaporation acceptable | Slow evaporation required (fragrance longevity, high-temp stability) |
| Humectancy | Strong humectant needed | Mild humectant, lighter feel preferred |
| Fragrance carrier | Acceptable but not ideal | Preferred — lower odor, better fragrance solvency |
| Regulatory (food/pharma) | FDA/USP approved — use PG | Not approved for food/pharma — use PG instead |
| Industrial (PU, resins) | Less common | Standard choice for PU and UPR production |
| Cost | Generally lower | Slight premium, especially fragrance grade |
For a detailed side-by-side comparison of the two compounds across all parameters, see our article on Propylene Glycol vs Dipropylene Glycol.
Safety and Handling
DPG has a low order of acute toxicity by oral and dermal routes. It is slightly irritating to eyes and skin in concentrated form but is well-tolerated in finished product formulations at typical use levels. It is not classified as a carcinogen, mutagen, or reproductive toxin under GHS. The flash point of 124°C means it is not classified as a flammable liquid under standard transport regulations, which simplifies logistics compared to alcohol-based solvents.
Storage: DPG is slightly hygroscopic and should be stored in sealed containers away from moisture. Contact with copper, copper alloys, and zinc should be avoided as these metals can catalyze degradation. Shelf life is 24 months in sealed containers; use within 12 months after opening.
Frequently Asked Questions
Is dipropylene glycol safe for skin?
Yes, at typical cosmetic concentrations. DPG is well-tolerated in personal care products and has a low irritation profile. It is not approved for food or pharmaceutical use, but for topical cosmetic applications it is considered safe. The Cosmetic Ingredient Review (CIR) has assessed DPG and concluded it is safe as currently used in cosmetics.
What is the difference between fragrance grade and industrial grade DPG?
Fragrance-grade DPG is refined to maximize the low-odor 2,2′-isomer and minimize odor-contributing isomers, with purity typically ≥99.5%. Industrial-grade DPG has a broader isomer mix and a faint but perceptible odor, with purity typically ≥98.0%. For perfumery and personal care, fragrance grade is required. For polyurethane production, resins, and other industrial uses, industrial grade is standard and more cost-effective.
Can DPG replace propylene glycol in formulations?
In some applications, partially. DPG can substitute for PG as a co-solvent or humectant in personal care, and it is a better fragrance carrier. However, DPG cannot replace PG in food, pharmaceutical, or injectable applications where PG holds regulatory approval. In industrial applications, the two serve different roles — DPG is preferred for PU and resin production, while PG is used in antifreeze, hydraulic fluids, and food-grade applications.
Why is DPG used in reed diffusers?
DPG’s combination of low viscosity, very low vapor pressure, and near-zero odor makes it ideal for reed diffusers. Its low viscosity allows it to wick efficiently up rattan reeds. Its very low vapor pressure means it evaporates slowly, releasing fragrance gradually over weeks rather than days. Its near-zero odor means it does not interfere with the fragrance composition. Propylene glycol evaporates faster and is stickier, making it less suitable for this application.
Conclusion
Dipropylene glycol is a straightforward material once you understand what it does well: slow evaporation, low odor, good solvency for fragrance materials, and reactivity as a diol in polymer chemistry. Those properties explain why it shows up in such different contexts — from a reed diffuser base to a polyurethane intermediate. The main sourcing decision is grade: fragrance grade for perfumery and personal care, industrial grade for everything else.
Niran Chemical supplies Dipropylene Glycol in fragrance and industrial grades, with COA, MSDS, and TDS available on request.
