Propylene Glycol Humidor Solution for Passive Humidifiers

A propylene glycol humidor solution is a 50/50 mix of propylene glycol and distilled water that you pour into a passive humidifying element. Simply Cigars, a UK retailer, sells it under the name "Cigar Humidification Solution."

Follow these steps:

1. Confirm your humidifier is a passive element and does not use silica gel beads.
2. Mix equal parts propylene glycol and distilled water, or use a premixed solution.
3. Rinse the element with distilled water and let it dry if it has held solution before.
4. Fill the element with the 50/50 mix and place it back in the humidor.
5. Close the lid and watch the hygrometer reading over the next few days.

Expect the reading to settle near 70 percent RH. The ideal range inside a humidor is around 68 to 72 percent, and humidity should never go higher than 75 percent. Some users on cigar forums report a humidity spike when a propylene glycol element is first used. These are unverified user reports, so watch the first readings closely.

You need a working hygrometer to see any of this. Our cigar hygrometers guide covers how to pick one.

Propylene glycol has a buffering effect on humidity, so a 50/50 solution keeps the air in a humidor at approximately 70 percent RH. That figure comes from the Wikipedia entry on humidors, which recommends the mix for replenishing passive humidifying elements.

Most humidifying elements are passive. They store moisture and release it through evaporation and diffusion.

Retailers describe the solution as self-regulating. Simply Cigars says it releases moisture when the air is dry and absorbs moisture when the air is humid. Neptune Cigar, a retailer, makes the same point: the solution both humidifies and absorbs excess humidity.

Retailers and manufacturers also claim propylene glycol has mild antifungal and antibacterial properties. Neptune Cigar calls it a mold and bacterial inhibitor. These are retailer claims, and the sources here do not establish them.

Distilled water lacks minerals, additives, and bacteria, which is why the sources say to always use it in a humidor.

Do not use propylene glycol in a humidifier built on silica gel beads. Those elements need only distilled water, and propylene glycol can ruin them.

Electronic humidifiers are a second case. They are usually reserved for very large humidors. A sensor measures humidity and switches on a ventilator that blows air over a humid sponge. They hold humidity more stably than passive elements and usually sound an alarm when the water supply needs refilling.

None of the sources here say propylene glycol is suitable for an electronic unit's water supply, so we would not add it. Fill electronic units with what their instructions specify. For a rundown of humidifier types, read our humidifier for humidor guide.

If you are still choosing a box and want one with a passive element, our best cigar humidors page lists our picks.

Recharge a propylene glycol element by first rinsing it with distilled water and letting it dry, which removes the leftover solution, then refilling it with fresh 50/50 mix. That rinse step comes from Neptune Cigar's maintenance tips.

Retailers give different intervals, and none of the sources agree on one number:

• Neptune Cigar: recharge with solution roughly every 1 to 3 months, or about every 6 months in some climates. Add only distilled water in between.
• Simply Cigars: check humidity every two weeks, and more often in dry climates or if the lid seal may leak. Never let the humidifier dry out completely.

Treat both as retailer guidance. Your hygrometer reading tells you when the element needs attention.

Forum users raise one more point about topping up. They report that only the water evaporates from the element, so adding more 50/50 mix gradually changes the ratio. Some of these users top up with plain distilled water and replace the whole solution every few months. These are unverified user reports, and they line up with Neptune Cigar's advice to add only distilled water between recharges.

Propylene glycol solution both adds and absorbs moisture, while distilled water alone only adds it. Humidity packs are a separate system that we cover in their own guide.

Criteria	50/50 propylene glycol solution	Distilled water alone	Humidity packs
What it does	Adds moisture and absorbs excess (retailer claim)	Only adds humidity	See our Boveda cigar humidity packs guide
Expected RH	About 70 percent	No target given in our sources	Covered in the pack guide
How often to check	Every two weeks (Simply Cigars)	More often than solution, per Simply Cigars	Covered in the pack guide
Silica-bead elements	Can ruin them	The only thing they need	Separate system
Seasoning a new box	Not the method Wikipedia describes	A small container for 1 to 3 days (Wikipedia)	Covered in our seasoning guide

Distilled water works in a passive element, but Simply Cigars notes it needs more frequent checks and refills because it only adds humidity. Our cigar humidity guide covers target ranges in more depth.

Once your element is filled, log your readings in the Humidor Tracker so you can see when the propylene glycol humidor needs its next recharge.