DIY Fog Fluid: How to Make Fog Machine Liquid (PG, Glycerin & DI Water)

What is fog juice made of?

Fog juice is water with one or more glycols or glycerin dissolved in it. Commercial water-based fluids use propylene glycol, triethylene glycol, butylene glycol or glycerin in deionized water, and ANSI E1.5, the industry standard for this fog, permits only water plus a short list of di- and trihydric alcohols. A homemade mix uses USP propylene glycol, USP glycerin, or both.

Makers rarely publish percentages: Rosco's Fog Fluid SDS lists triethylene glycol, 1,3-butylene glycol, propylene glycol and deionized water with no amounts. "Smoke fluid" for a smoke machine is the same chemistry; nothing burns.

The Science of Fog Generation

Fog machines make fog with a pump, a heater and a nozzle. The pump pushes fog fluid into an electrically heated block (the heat exchanger), the fluid flashes to vapor, and the vapor leaves the nozzle into cooler room air, where it condenses into fine droplets of glycol or glycerin. The glycols then evaporate rapidly from the droplet surfaces, so the droplets shrink and the fog eventually vaporizes completely; how fast depends on the fluid, temperature and humidity (Mount Sinai and ENVIRON study for the Equity-League trust funds).

Makers rarely publish heater temperatures. NIOSH (HETA 90-0355-2449) reported, from manufacturer information, that Broadway fog machines heated glycol fluids to about 290 to 370 °C (554 to 700 °F). In NIOSH's lab test, aldehyde breakdown products appeared only in the fluid heated to about 700 °F (none were found in theater air), so NIOSH recommended heating fluid only as hot as proper fog requires.

The chemical composition of your fog fluid directly controls every visual property of the fog: density, opacity, hang time, particle size, and even how light interacts with the cloud. Propylene glycol (PG) and glycerin (vegetable glycerin or VG) are the two primary active ingredients in virtually all commercial and DIY fog fluids, with deionized water serving as the carrier solvent. Each ingredient contributes unique physical properties that, when combined in specific ratios, allow you to engineer fog effects ranging from a barely visible atmospheric haze to a dense, opaque ground-hugging mist.

Understanding the thermodynamics is straightforward: propylene glycol has a boiling point of 370 °F (188 °C) and glycerin boils at 554 °F (290 °C). Water boils at 212 °F (100 °C). When your fog machine heats the blended fluid, water vaporizes first, carrying PG and glycerin molecules with it. The glycol and glycerin then condense in the cooler air, forming the visible droplets. Higher glycerin ratios produce larger, heavier droplets — hence denser, lower-lying fog. Higher PG ratios yield finer droplets that disperse more evenly, creating an ethereal haze.

Boiling point, flash point and density: PG vs. glycerin

Sources: PubChem CID 1030, CID 753; NIST WebBook (PG, glycerin).

Key Ingredients: PG, Glycerin & DI Water

Propylene Glycol (PG) — The Fog Enhancer

Propylene glycol (C₃H₈O₂) is a colorless, viscous, nearly odorless liquid affirmed by the FDA as Generally Recognized as Safe (GRAS) for use in food (21 CFR 184.1666). That covers eating it, not breathing it (see toxicity). It is the backbone of most commercial fog fluids, prized for producing a fine, evenly dispersed aerosol that hangs in the air for moderate periods. PG-dominant fog creates a smooth, luminous haze that scatters light beautifully — perfect for laser shows, stage lighting, and atmospheric effects. For a deeper dive into PG applications, see our article on propylene glycol food-grade applications.

PG is hygroscopic, meaning it absorbs moisture from the surrounding air; how long glycol fog lasts depends on the fluid, temperature and humidity (Equity study, above). Its relatively low viscosity compared to glycerin means PG-based fluids flow easily through fog machine pumps and heat exchangers, reducing wear and maintenance requirements. Alliance Chemical offers Propylene Glycol USP Grade.

Glycerin (VG) — The Dense Fog Creator

Glycerin (C₃H₈O₃), also known as glycerol, glycerine or vegetable glycerin (VG), is a thick, sweet-tasting, colorless liquid derived from vegetable oils. In fog-making, glycerin produces larger, heavier aerosol droplets compared to PG, resulting in denser, more opaque fog that tends to settle lower to the ground. This makes glycerin the ingredient of choice for dramatic low-lying mist effects reminiscent of classic horror film atmospheres.

Glycerin is an excellent humectant — it draws and retains moisture from the environment — which enhances fog stability in dry conditions. Its higher boiling point (554 °F vs. PG's 370 °F) means glycerin requires more heat to fully vaporize, making the fluid composition especially important in machines with different heat output ratings. Understanding chemical grades matters here: NIOSH recommended high-purity glycols for theatrical fog, and for fog people will breathe we recommend Glycerin USP Grade.

Deionized Water — The Pure Carrier

Deionized (DI) water serves as the carrier solvent that dilutes PG and glycerin to their optimal concentrations and facilitates even heat transfer within the fog machine. DI water is produced through ion-exchange processes that remove dissolved salts and minerals, yielding a purity level far exceeding tap or even standard filtered water. For fog-making, this purity directly translates to cleaner machine operation, reduced maintenance, and more consistent fog output over time.

PG vs. Glycerin vs. Blended Fog Fluids

Choosing between propylene glycol, glycerin, or a combination depends on your desired fog effect, machine type, and environmental conditions. Here is a detailed comparison of the three approaches:

Fog Machine Types & Fluid Requirements

Not all fog machines are created equal, and using the wrong fluid in the wrong machine can result in poor output, excessive residue, or even damage. Understanding your machine type is essential to selecting (or mixing) the correct fog fluid. If you handle chemicals regularly, review our chemical storage guide for proper fluid storage between uses.

Can you make your own fog machine?

Yes, in principle, but buy a listed commercial machine instead. A fog machine is a fluid tank, a small pump, a temperature-controlled heater block and a nozzle; a homemade heater usually lacks that control, and in NIOSH's lab test glycol fluid heated to about 700 °F gave off aldehyde breakdown products. Choose a unit with a recognized safety listing such as UL or ETL and follow its manual for fluid and duty cycle.

DIY Fog Fluid Recipes for Every Effect

Below are seven starting formulas, ordered by total active (propylene glycol plus glycerin) from atmospheric haze at 15% to ground fog at 45%. All recipes assume a 1-gallon (3.78 L) final batch. Use only USP-grade propylene glycol and glycerin and deionized water.

How to make fog juice with glycerin (or with propylene glycol only)

For glycerin fog juice, mix 1 part USP glycerin with 4 parts deionized water (20% active, Glycerin Light Fog) or 1 part with 3 (25%, Glycerin Heavy Fog). For propylene glycol only, use 15% for haze or 1:4 (20%, PG Light Fog); for the densest fog, the blended Dense Halloween Fog runs 40% active. All of these are hobbyist starting points, not numbers from a standard or a machine maker.

How to make haze fluid, and how haze differs from fog

Water-based haze fluid is a lean glycol mix: the Atmospheric Haze recipe, 15% USP propylene glycol in deionized water, is a common starting point. Fog is a dense, local cloud you are meant to see; haze is a thin, even atmosphere, kept topped up by a hazer, that makes light beams visible without hiding the stage.

Step-by-Step Mixing Guide

Creating your own fog fluid is straightforward, but precision matters. Incorrect ratios can result in thin, disappointing fog or excessive residue that coats surfaces and clogs your machine. Follow these steps for consistent, professional-quality results:

1. Gather ingredients and equipment: You will need deionized water, USP-grade propylene glycol, USP-grade glycerin, a clean mixing container (glass or HDPE plastic), measuring cylinders or a kitchen scale, and a stirring rod or whisk.
2. Calculate your recipe volumes: Choose your target recipe from the table above. For a 1-gallon batch of Standard Stage Fog, measure 2.65 L of DI water, 757 mL of propylene glycol, and 378 mL of glycerin.
3. Start with DI water: Pour the measured deionized water into your clean mixing container. Starting with water ensures even dissolution of the glycols.
4. Add propylene glycol: Slowly pour the propylene glycol into the water while stirring gently. PG is fully miscible with water and should dissolve quickly into a clear, uniform solution.
5. Add glycerin (if using): Pour glycerin into the solution while continuing to stir. Glycerin is more viscous than PG, so stir thoroughly for 2–3 minutes until no visible striations remain and the fluid looks perfectly clear and uniform.
6. Test a small amount: Pour approximately 200 mL into your fog machine, allow full heat-up, and run a 10-second burst. Evaluate density, hang time, and residue levels. Adjust your formula if needed before mixing the full batch.
7. Store properly: Transfer the finished fluid to a clean, labeled, airtight container. Store in a cool, dark location away from direct sunlight. Mix what you will use this season; discard any batch that turns cloudy or smells off, and do not leave fluid sitting in the machine's tank (the Chauvet manual's limit is 10 days).

Applications Beyond Halloween

While Halloween haunts and spooky graveyards may be the most iconic use case, fog fluid technology serves a remarkably diverse range of industries and applications. The same chemistry that conjures spectral mist for trick-or-treaters also plays critical roles in professional entertainment, safety training, horticulture, and scientific research.

The versatility of glycol-based fog fluid underscores the importance of starting with high-purity, properly graded chemicals. Whether your fog will be inhaled by concert-goers or used to train first responders, ingredient quality directly impacts safety and performance. For industries that also use industrial solvents, the sourcing principles are identical: purity, consistency, and traceability.

What should you never put in a fog machine?

Four substitutes circulate in DIY threads and hardware-store aisles. Each one damages the machine, the room, or the people in it. This is the part most recipe posts leave out.

Baby oil and mineral oil

A water-based fog machine drives fluid across a heater block built to flash water and glycols to vapor. Mineral oil and baby oil are petroleum distillates: they are not miscible with water, they do not flash to a clean vapour in that heater, and they leave a varnish on the heat exchanger that eventually chokes the machine and creates a scorching hazard. Oil mist is also treated as its own occupational exposure category — OSHA sets a separate permissible exposure limit for mineral oil mist — which is why oil-based haze uses purpose-built crackers with their own fluid, not a repurposed fog machine. If you own a water-based machine, oil is not a substitute for fog fluid.

Tap water

Tap water carries dissolved calcium and magnesium. Every heating cycle leaves those minerals behind on the heat exchanger as scale, which narrows the channel, reduces output and eventually blocks it entirely. This is the single most common cause of a fog machine that "just stopped working." Use deionized or distilled water for both the mix and the end-of-season flush.

Is fog machine liquid toxic or safe to breathe?

Most ECHA notifiers report that neither propylene glycol nor glycerin meets GHS hazard criteria, but studies link heavy or close-range fog exposure to airway irritation. ANSI E1.5, the entertainment-industry standard, considers this fog unlikely to harm healthy people aged 18 to 64 when the breathing-zone level stays at or below 10 mg/m³ averaged over 8 hours and never tops 40 mg/m³ (50 mg/m³ for glycerin alone).

• Mount Sinai School of Medicine and ENVIRON for the Equity-League Pension and Health Trust Funds (2000): 439 actors, 16 Broadway musicals. No evidence of serious health effects, but peak glycol exposures were associated with respiratory, throat and nasal symptoms and vocal-cord inflammation; the authors recommended a 40 mg/m³ peak ceiling for glycols.
• NIOSH HETA 90-0355-2449 (1994): no evidence that theatrical "smoke" at measured levels caused occupational asthma, but glycols could irritate or dry mucous membranes. NIOSH recommended moving machines away from performers, using the least fog needed, maker-approved fluids, and the lowest workable heater temperature.
• Varughese et al., American Journal of Industrial Medicine (2005): 101 workers, 19 sites. Cough and dry throat were associated with glycol fog, chronic wheeze and chest tightness with cumulative fog exposure, and lung function was lower closest to the source.

What that means for a home or haunt setup

• Distance controls peaks. The Equity study tied symptoms to peaks, not total dose, and noted that peaks are largely independent of ventilation. Keep people, especially anyone with asthma, out of the plume near the nozzle.
• The limits cover healthy adults 18 to 64 only. ANSI E1.5 makes no statement about children or older people.
• Finished fluids carry warnings. Rosco's fog fluid SDS lists mild skin irritation, eye irritation and possible respiratory irritation, and a 10 mg/m³ AIHA workplace guideline (WEEL) for propylene glycol. OSHA's limit for glycerin mist is 15 mg/m³ total, 5 mg/m³ respirable (8-hour average). Read the SDS for the product you buy.

Safety & Handling Best Practices

Hazard class and exposure limits are in the toxicity section above. Responsible handling, proper ventilation, and awareness of potential hazards are essential for any fog operation. Review our comprehensive guide on chemical safety for foundational principles.

Ventilation Requirements

Dense fog can reduce visibility and, in enclosed spaces, may cause mild respiratory irritation for sensitive individuals. Always ensure adequate air exchange in indoor venues. For large-scale fog use (concerts, haunted houses), use mechanical ventilation to keep the average level down, and remember that ventilation does little for the peak near the nozzle, so keep people out of the plume. Open at least two exits or windows for cross-ventilation in smaller venues. Post signage alerting guests to fog use, especially where children, elderly, or asthma-susceptible individuals may be present.

Ingredient Handling

When handling concentrated PG and glycerin, wear appropriate PPE: chemical-splash safety goggles and nitrile or latex gloves. Concentrated glycerin is extremely slippery when spilled, creating a significant slip hazard. Clean spills immediately with absorbent material and warm water.

Machine Safety

• Never operate a fog machine unattended — monitor temperature, fluid level, and output continuously
• Allow adequate warm-up and cool-down time: use the warm-up your manual states and wait for the ready light; the two manuals cited here give 2 to 5 minutes (Chauvet Hurricane 1000: 2 minutes in its specifications, up to 3 to 4 minutes in its operating steps; Home Accents Holiday 1000 W: 3 to 5 minutes)
• Do not overfill the reservoir — leave headspace for fluid expansion as temperature rises
• Clean the machine the way its manual says. Chauvet's Hurricane 1000 manual, for example, calls for Chauvet fog cleaner every 30 to 90 days, then at least 30 seconds of distilled water, and no fluid left in the tank over 10 days. Do not improvise a vinegar or other cleaner unless your manual calls for it.
• Inspect power cords and connections — fog machines operate at high wattages; damaged cords are a fire hazard
• Keep machines elevated and stable: place on a flat, heat-resistant surface with the clearance your manual specifies (the Chauvet Hurricane 1000 manual asks for at least 20 inches of ventilation space), away from flammable materials

Troubleshooting Common Problems

Even with the right fluid and equipment, fog production can sometimes disappoint. Here are the most common issues and their solutions:

Problem: Thin, Sparse Fog That Disappears Quickly

Causes: Fluid ratio too dilute (too much water), low ambient humidity, machine not reaching full operating temperature, or nozzle partially clogged.

Fix: Increase glycerin a few percent (a starting adjustment, not a published figure). Verify the machine has fully heated (wait for the "ready" indicator). Clean the nozzle with DI water and a soft cloth. In dry environments, a nearby misting fan can raise local humidity.

Problem: Excessive Residue on Surfaces

Causes: Too much glycerin in the formula, machine temperature too low (incomplete vaporization), or ingredients with additives or impurities.

Fix: Reduce glycerin a few percent or switch to a PG-dominant formula. Ensure you are using USP-grade glycerin free of additives. Wipe affected surfaces with a solution of isopropyl alcohol 99% diluted 1:3 with water.

Problem: No Fog Output at All

Causes: Empty reservoir, failed heating element, air lock in the pump line, or power supply issue.

Fix: Check fluid level. Confirm the power indicator is lit and the outlet provides stable voltage. Prime the pump by running a short burst cycle. If the heating element has failed, consult the manufacturer for replacement parts.

Problem: Machine Overheating or Auto-Shutoff

Causes: Continuous operation beyond duty cycle, blocked ventilation ports, or fluid with too-high glycerin concentration forcing the heater to work harder.

Fix: Follow the duty cycle in your manual (Chauvet's Hurricane 1000: no more than 15 minutes continuous, then an equal rest; the Home Accents machine pauses 1 to 2 minutes to reheat after each blast). Clear any obstructions from machine vents. Reduce glycerin if you are running a high-glycerin recipe (Dense Halloween or Low-Lying) in a machine whose manual does not call for dense fluid.

Problem: Fog Has an Off Odor or Taste

Causes: Contaminated fluid, mineral-laden water, degraded/expired glycols, or a heater running too hot.

Fix: Discard the batch and start fresh with clean deionized water and unopened USP-grade PG and glycerin. Run the cleaning procedure in your machine's manual before refilling.

Environmental & Storage Considerations

Both propylene glycol and glycerin break down readily in standard sewage-sludge tests, and PubChem rates their potential to build up in aquatic organisms as low (an estimated bioconcentration factor of 3 for each). Rosco's fog fluid SDS says the finished fluid is not expected to be harmful to aquatic organisms. None of that replaces local disposal rules (see Disposal below). Our overview of green chemistry principles provides broader context for environmentally conscious chemical use.

Proper Storage

• Store fog fluid in HDPE or glass containers with tight-sealing lids in a cool place
• Keep away from direct sunlight, which can degrade glycols over time
• Label all containers with contents, date of preparation, and ratio used
• No published shelf life: mix what you will use this season and discard any batch that turns cloudy or smells off
• For bulk ingredient storage, follow our chemical storage guide for labs

Disposal

Disposal rules for dilute glycol solutions are set locally. Check with your wastewater utility before pouring any fog fluid down a drain, and for larger volumes or commercial operations follow the disposal protocols in our guide on how to dispose of chemicals safely. Never pour glycols into storm drains or natural waterways.

Energy-Efficient Fog Operations

Fog machines are high-wattage appliances (the two cited here draw 740 W and 1000 W). To minimize energy consumption: use timers or smart plugs to activate machines only during peak scare windows, pair fog machines with LED lighting (which generates far less heat than halogen), and maintain your machine regularly to ensure the heating element operates at maximum efficiency. A well-maintained machine reaches operating temperature faster and uses less energy per fog burst.

Frequently Asked Questions

What liquid goes in a fog or smoke machine?

The fluid its manual specifies. For a standard heated fog or smoke machine that is a water-based fog fluid: deionized water with propylene glycol, glycerin or both, which is what the recipes above make. Never use ethylene glycol antifreeze, baby oil or mineral oil, and plain water gives only a brief puff of steam. A cracked-oil hazer is the one machine type built for mineral oil.

Is fog fluid safe to breathe?

Not risk-free. See the toxicity section above for the ANSI E1.5 limits and what the Broadway and worker studies found.

Can I use tap water instead of deionized water?

Technically yes, but it is strongly discouraged. Tap water contains dissolved minerals that will accumulate inside your fog machine's heat exchanger, reducing efficiency and eventually causing failure. Mineral deposits also create inconsistent fog output and can introduce unwanted particles. Deionized water costs very little per batch and dramatically extends machine life.

Can you put just water in a fog machine?

Not as a fog fluid. Plain distilled water gives only a brief puff of steam that disappears within seconds, because there is no glycol or glycerin to form lasting droplets. Its job is cleaning: the two manuals cited here use distilled water as a rinse or as the cleaning run.

How long does a gallon of fog juice last?

It depends on the machine; check the run time in your manual and scale it. The Home Accents Holiday 1000 W manual says 1 liter runs about 100 minutes before the tank is empty, roughly 6 hours per gallon (3.78 L), with 1 to 2 minutes of reheating between blasts. Chauvet's Hurricane 1000 manual limits continuous output to 15 minutes followed by an equal rest and notes that consumption rises in continuous mode.

Does homemade fog fluid damage fog machines?

It can. Machine makers specify their own fluid (the Chauvet Hurricane 1000 manual does, and lists incorrect fluid as a cause of no output), and NIOSH recommended fluids approved by the machine maker. Use deionized water, clean the machine per its manual, and check your warranty terms before running a homemade mix.

What is the difference between fog and haze fluid?

Fog fluid is designed for visible, dense clouds — typically containing both PG and glycerin. Water-based haze fluid is a leaner PG mix (about 15% in the Atmospheric Haze recipe above), and many hazers run an oil-based fluid made for that machine instead. Haze is meant to catch light beams rather than obscure visibility, and a hazer keeps it topped up. Using fog fluid in a hazer, or vice versa, can result in poor performance.

Can I add scent or color to fog fluid?

Do not add scent or color. ANSI E1.5 says fogs made with scents or coloring agents do not meet the standard, and machine manuals (Chauvet's, for one) say not to add perfume, alcohol or any other chemical to the fluid. Colored lighting is the way to get colored fog.