Propylene glycol and ethylene glycol are often grouped together because both are industrial glycols used in heat transfer, manufacturing, and formulation work. That does not make them interchangeable. For food, pharmaceutical, and cosmetic applications, the difference is critical.
This guide draws the line clearly for buyers. Propylene glycol is selected where low toxicity and approved grades matter. Ethylene glycol, also called mono ethylene glycol or MEG, is selected where performance and cost matter in non-food industrial systems.
At a Glance — Key Differences
| Property | Propylene Glycol (PG) | Ethylene Glycol (MEG) |
|---|---|---|
| CAS | 57-55-6 | 107-21-1 |
| Toxicity | GRAS for approved food uses | Toxic if ingested |
| Boiling Point | 188°C | 197°C |
| Viscosity | Higher | Lower |
| Cost | Higher | Lower |
| Applications | Pharma, food, cosmetics, HVAC | Antifreeze, PET, textiles |
Where PG is the Right Choice
Pharmaceutical excipient: Propylene glycol is used in oral, topical, and selected injectable formulations when USP, BP, IP, or other approved pharma grades are specified. It acts as a solvent, humectant, and carrier.
Food processing: PG is used as a humectant and carrier in approved food applications. Buyers must specify food grade or other applicable compliance standards. Industrial PG should not be used in food applications without QA approval.
Cosmetics and personal care: PG appears in creams, lotions, fragrances, deodorants, and hair-care products as a moisturiser base, solvent, and carrier.
Food-safe HVAC systems: PG-based heat transfer fluids are preferred where incidental contact or food-adjacent risk makes MEG unacceptable.
Where MEG is the Right Choice
Automotive antifreeze coolant: MEG is widely used in engine coolants because it provides effective freeze protection and heat transfer.
PET resin manufacturing: MEG is a major feedstock for polyester and PET resin, including packaging and fibre applications.
Textile fibre processing: MEG is part of the polyester chain and appears in fibre-related industrial supply lines.
Industrial heat transfer: MEG can be used in non-food heat transfer systems where toxicity risk is controlled and site procedures allow it.
Can They Be Substituted?
The hard rule is simple: never substitute MEG for PG in food, pharmaceutical, or cosmetic applications. MEG is toxic if ingested and is not suitable for these uses.
For industrial HVAC and non-food heat transfer, either glycol may be technically possible, but the system must be reformulated and checked for viscosity, corrosion inhibition, pump performance, operating temperature, elastomer compatibility, and safety policy.
SPC Supplies Both
SPC Chennai stocks propylene glycol in industrial and USP grades, along with mono ethylene glycol, diethylene glycol, and polyethylene glycol grades such as PEG 200, PEG 400, and PEG 600. Availability varies by grade and packing.
Get a Glycol Recommendation
For PG, MEG, DEG, or PEG requirements, share your application, grade, quantity, packing, and delivery location. Call or WhatsApp Sudarshan Bohra at +91 81979 47045, email Admin@supremepetrochemicals.com, or use the SPC enquiry form.