Picture two clear liquids sold under the same name. One touches skin and tongue in baby shampoo and cough syrup; the other boils inside a polyurethane resin reactor. Both are labelled "propylene glycol." The difference is not hidden in a word — it lives in a document: the purity grade. A buyer who orders the wrong grade either overpays or commits a compliance error that cannot be undone once the product ships across a border.
What Is Monopropylene Glycol (MPG)?
Monopropylene glycol (MPG) — chemical name propane-1,2-diol, CAS 57-55-6 — is a clear, colorless, practically odorless and slightly sweet liquid. Its diol structure (two hydroxyl groups) makes it fully miscible with water and with many organic solvents. That combination of hygroscopic and solvent behavior is exactly what makes MPG one of the most versatile raw materials on a distributor's shelf.
Industrially it is produced by the hydration of propylene oxide. On the market you will also see it as "propylene glycol," "1,2-propanediol," or simply PG. The "mono" prefix signals a single propylene unit in the molecule, distinguishing it from the di- and tri- oligomers (dipropylene glycol, tripropylene glycol).
The single most important property of MPG is that, unlike monoethylene glycol (MEG), it has low toxicity and — when produced to the right purity — can be used in food, cosmetic and pharmaceutical applications. A plant that does not understand this distinction can accidentally specify MEG in a contact-risk product and create a serious safety gap. That is why our MEG vs MPG comparison is the natural starting point for anyone about to make a sourcing decision.
Key Physical and Chemical Properties
Below are the parameters our technical team and customers reference most often, gathered in a single table:
| Property | Typical Value | Note |
|---|---|---|
| CAS number | 57-55-6 | Single, fixed identity |
| Chemical name | Propane-1,2-diol (1,2-propanediol) | "Propylene glycol" is the trade name |
| Molecular weight | ~76.09 g/mol | — |
| Density (20 °C) | ~1.036 g/cm³ | Slightly heavier than water |
| Boiling point | ~187–188 °C | Lower than MEG |
| Freezing/pour point | ~ -59 °C | Effective freeze protection |
| Flash point | ~99 °C (closed cup) | Low flammability class |
| Viscosity (20 °C) | ~48–60 mPa·s | More viscous than MEG |
| Water solubility | Fully miscible | Hygroscopic |
| Appearance | Clear, colorless liquid | Odorless, faintly sweet |
These figures are for typical commercial MPG; always confirm the real values of the batch you receive against its COA (Certificate of Analysis). If you want to benchmark MPG against the rest of the glycol family for identity and freeze-protection performance, the spec tables in our what is monoethylene glycol guide are a useful reference.
MPG Purity Grades: Industrial, USP and Food
When you buy MPG, the first question is not "how many kilos?" but "which grade?" A product with the same CAS number serves completely different markets depending on its purity and impurity profile — and the price moves accordingly.
Here are the three main grades and the practical points that separate them:
| Grade | Typical Purity | Conformity Reference | Typical Use | Critical Impurity Control |
|---|---|---|---|---|
| Industrial | ≥ 99.5% | Technical spec / house standard | UPR resin, antifreeze/coolant, solvent, aircraft de-icing | Wider tolerance on DPG and water |
| USP/EP (Pharma) | ≥ 99.5% (USP-NF) | USP-NF / Ph. Eur. monograph | Pharmaceuticals, oral/topical formulation, e-liquid | Tight limits on heavy metals, DPG, impurities |
| Food (FCC) | ≥ 99.5% (FCC) | FCC / food-contact declaration | Humectant, flavor carrier, food additive | Documented food-contact suitability |
In practice, USP and food grade are often produced in the same high-purity band; the distinction comes down to which monograph or document the batch is released against and which set of impurity limits applies. Industrial grade, while pure enough for resin and antifreeze applications, is not suitable for food or pharmaceutical contact and cannot be sold as such.
Verify the Grade with Documents, Not by Eye
You cannot distinguish two clear, odorless liquids without a laboratory. That is why the grade is always confirmed with the COA + SDS + declaration of conformity trio:
- COA (Certificate of Analysis): batch-level actual purity, DPG content, water, acidity and color (APHA) values.
- SDS (Safety Data Sheet): hazard classification, transport and storage conditions — essential documentation for cross-border shipments and customs clearance.
- Declaration of conformity: conformity to USP-NF, Ph. Eur. or FCC; and the relevant declaration for food-contact uses.
The most expensive mistake we see in the field is buying industrial MPG because it is cheap and then slipping it into a food or cosmetic formulation. When an auditor asks for the paperwork, the cost of that compliance gap dwarfs the price difference between grades. For export buyers this risk is amplified: a rejected shipment at destination means demurrage, re-testing and a damaged relationship, not just a credit note.
MPG Uses
Monopropylene glycol is one of those rare raw materials that refuses to stay in a single sector. The same molecule holds moisture in food, protects an engine from freezing in a car, and builds chains inside a resin reactor. Let us look at the main uses alongside the grade each one requires.
Humectant in Food and Beverage
Food/FCC grade MPG works as a humectant and a flavor/color carrier. In cake fillings, soft confectionery, glazes and certain baked goods it prevents the structure from drying out and extends shelf life. In flavor and color concentrates it acts as a carrier that distributes poorly water- or oil-soluble components evenly.
The critical point here: only food/FCC grade may enter a food application, and dosage is subject to the limits set by the local food regulations of the destination market. Industrial grade never enters this space.
Moisturizer in Cosmetics and Personal Care
In cosmetics, MPG (INCI name "Propylene Glycol") is widely used as a humectant, solvent and emollient. In creams, lotions, deodorants, shampoos and makeup removers it helps retain the skin's water content and dissolves active ingredients. Its hygroscopic nature slows the formulation from drying out.
For cosmetic applications, USP/EP grade or a cosmetic-purity product is generally preferred; impurity and heavy-metal limits matter here because of skin contact.
Pharmaceuticals and E-Liquid (Pharma Grade)
USP/EP grade MPG is used in the pharmaceutical industry as a solvent and carrier excipient: oral syrups, topical preparations and some injectable formulations. The same pharma grade is one of the main components of the e-liquid base, usually blended with vegetable glycerin (VG) at defined ratios. Industrial grade is absolutely not accepted in these applications; USP-NF conformity and a COA are mandatory.
Low-Toxicity Antifreeze and Heat-Transfer Fluid
MPG's freezing point down to -59 °C, combined with its low toxicity, makes it ideal for heat-transfer and freeze-protection duties that carry a contact risk: cooling circuits in food plants, solar thermal systems, HVAC, aircraft de-icing fluids and loops near potable water systems.
Here the distinction from MEG is vital. MEG is toxic; it is avoided anywhere a leak could contaminate food or drinking water. We cover these safety-driven choices in MEG vs MPG and, on the classic automotive side, the trade-off between the two glycols matters most when a coolant loop can reach a heat exchanger shared with a food or water stream.
Unsaturated Polyester Resin (UPR) and Industrial Solvent
Industrial grade MPG enters the chain structure as the diol component in unsaturated polyester resin (UPR) production; these resins are common in glass-fiber-reinforced plastics, boat hulls and composite products. It also serves as a solvent and humectant in paints, inks and cleaning formulations. The rest of the glycol family — diethylene glycol, triethylene glycol — steps in for entirely different jobs such as gas dehydration and plasticizing, which we gather in our diethylene and triethylene glycol guide.
MPG vs MEG: Why the Toxicity Difference Is Decisive
Both glycols are clear, odorless, faintly sweet liquids and physically similar. But there is a chasm between them on toxicity, and that chasm sits at the center of the purchasing decision.
| Criterion | MPG (Propylene Glycol) | MEG (Ethylene Glycol) |
|---|---|---|
| CAS number | 57-55-6 | 107-21-1 |
| Toxicity | Low; metabolized to lactic acid | Markedly toxic; metabolized to oxalic acid |
| Food/pharma use | Suitable (USP/FCC grade) | Not suitable |
| Contact-risk antifreeze | Preferred | Not recommended |
| Viscosity | Higher | Lower |
| Boiling point | ~187 °C | ~197 °C |
| Typical cost | Generally higher | Generally lower |
In short: you cannot put MEG everywhere just to keep the cost down. Wherever there is human contact, food contact or proximity to drinking water, MPG's low toxicity is not a luxury but a requirement. The other glycol derivatives (diethylene glycol, triethylene glycol) come into play for entirely separate tasks — moisture scavenging, gas drying and plasticizing — which we cover in our diethylene glycol and triethylene glycol article.
Storage, Packaging and Transport
Although MPG has a low hazard profile, its hygroscopic nature and flammability class mean the right conditions still matter — especially over long export transit times.
- Packaging: typically offered in HDPE drums (5–30 kg), 200–230 kg barrels, ~1000 L IBC (totes) and bulk tanker options. For international orders, IBCs and drums travel well in standard containers, while bulk suits high-volume contract buyers.
- Storage: in a cool, dry, well-ventilated area, in closed containers. Because it is hygroscopic, leaving the lid open draws in moisture and lowers purity.
- Compatibility: the suitable materials are HDPE and stainless steel; keep away from oxidizers.
- Transport and labelling: follow the relevant hazard/labelling rules for the shipping mode. For sea freight and land legs, align the SDS classification with your Incoterms and destination import requirements before the container is booked.
Shelf Life and Quality Tracking
Correctly stored MPG has a long shelf life; but because it is hygroscopic, water content rises over time in open containers, and that can compromise both freeze-protection performance and food/pharma conformity. Confirming water content and purity via the COA on every new batch prevents most of the quality problems we see in the field — a discipline that matters even more when material has spent weeks in a container crossing several climate zones.
Choosing the Right MPG Grade: A Decision Guide
For any purchase, answering these three questions in order eliminates most mistakes:
- Will the product contact humans or food? If yes, food/USP grade; if no, industrial grade may be sufficient.
- Which document must it conform to? The monograph your formulation or your customer demands (USP-NF, Ph. Eur., FCC) determines the grade.
- What packaging and volume? Drum/IBC/bulk and annual volume drive both the logistics and the unit cost — and, for export, the Incoterms you should quote against.
When selecting a supplier, document transparency, batch traceability and technical support are decisive. As a distributor based in Kestel, Bursa, Turkey, we supply MPG and glycol derivatives with the export documentation international buyers need — COA, SDS and conformity declarations aligned to the destination market.
At Yüksek Kimya we supply MPG and glycol derivatives across industrial and higher-purity requirements in a range of packaging options. From automotive to textile, packaging to paint and coatings, you can see the full portfolio in our glycols and derivatives product category.
Request a Quote or Sample
MPG price depends on the purity grade (industrial/USP/food), packaging type, order volume and current feedstock/currency conditions — and, for export, on Incoterms and destination documentation. For this reason we work with a project-specific quotation model rather than a fixed online price.
To move forward with the right grade at the right price, send us the grade you need, your estimated quantity and your packaging preference, and we will provide a current quote together with the relevant SDS and COA documents. We also handle sample requests. For quotes and any questions, reach us through our contact page; our team will be glad to help you identify the MPG grade best suited to your application and export market.
Related reading
Frequently Asked Questions
Is monopropylene glycol (MPG) toxic?
You have to separate industrial MPG from food/USP grade. Propylene glycol itself has low toxicity and is metabolized into lactic acid in the body, which is why USP/food grade is treated as GRAS by the FDA. Industrial grade, however, is not suitable for food or pharmaceutical use because of its purity and impurity profile. In all cases MPG is far safer than ethylene glycol (MEG).
What is the difference between MPG and MEG (monoethylene glycol)?
MEG is markedly toxic and can cause kidney failure if ingested, while MPG has low toxicity and is approved for food, cosmetic and pharmaceutical use. Physically, MPG is more viscous and has a slightly lower boiling point. Where there is any contact risk, MPG is the preferred antifreeze base. See our MEG vs MPG article for a detailed side-by-side comparison.
How do I tell food grade and industrial MPG apart?
You cannot tell them apart by eye — the difference lives in the paperwork. Food/USP grade ships with conformity to a USP-NF or EP monograph, a matching COA and a food-contact declaration, with tight dipropylene glycol and impurity limits. Industrial grade has looser limits. Always request the COA and SDS before you commit to a grade.
What does MPG pricing depend on?
MPG price depends on the purity grade (industrial/USP/food), packaging type (drum, IBC, bulk), order volume and the underlying propylene oxide feedstock and currency conditions. There is no fixed online price. For export orders, Incoterms and destination documentation also affect the landed cost, so the fastest route to an accurate quote is to send us your grade, quantity and packaging needs.