Propylene Glycol USP is the thin, clear, USP grade carrier liquid that gets blended with vegetable glycerin in aromatherapy diffuser and refill liquids. On its own it is far thinner than glycerin, so it carries flavor and essence well and keeps a blend from being too thick to wick. It is the same grade we use in our own refill liquids, repacked from bulk gallons.
 
At a glance
USP grade, 99.5% minimum purity, food grade
No additives, no water, no fragrance
Thins glycerin blends and carries flavor and essence
Also used as a solvent for plant compounds that do not dissolve well in water or alcohol
Sold in 8 oz, 16 oz and 32 oz
 
What it is. Propylene glycol is a clear, nearly odorless liquid used in food, cosmetics and pharmacy work. USP grade means it is purified and tested to pharmacopeia standard, which is not the same as the industrial or antifreeze grades sold at hardware stores. Do not substitute those.
 
How to use it. Most diffuser liquids sit somewhere between 50/50 and 70/30 vegetable glycerin to propylene glycol by volume. More glycerin gives a thicker liquid and denser vapor. More propylene glycol gives a thinner liquid that wicks faster and carries flavor harder. Start at 50/50, mix well, and adjust on the next batch. It also works as a solvent for concentrated extracts before they go into a glycerin base, since it blends with both water and glycerin in any ratio.
 
Goes with. Fill the finished blend into empty 0.5 ml 510 cartridges and run them on a 510 thread battery, or split it into 30 ml squeeze bottles. Clean the threads and the bench after with 99% isopropyl alcohol. The rest is in Accessories and DIY Supplies.
Specs. Grade: USP, food grade. Purity: 99.5% minimum. Form: clear, colorless, low-viscosity liquid, faintly sweet. Weight: about 1.04 kg per liter. Shelf life: several years capped at room temperature out of sunlight. Packaging: 8 oz, 16 oz or 32 oz bottle with a sealed cap.
 
Common questions
Is this food grade? Yes, USP food grade. It is not the industrial or antifreeze grade.
How should I store it? Capped, at room temperature, out of sun. It does not go bad in any practical time frame.
 
Disclaimer. Sold as a raw ingredient. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease. Keep out of reach of children. For adults 21 and over.