A vape turns liquid into an inhalable aerosol by heating it with a small electric coil, typically to temperatures between 157°C and 266°C (315–510°F). The process is surprisingly simple: a battery sends current through a metal heating element, that element heats a liquid-soaked wick, and the liquid vaporizes into a fine mist you inhale. But the details of each step, from the chemistry of the liquid to what happens at high temperatures, matter more than most users realize.
What Happens When You Inhale
Most modern vapes don’t have a button. Instead, they use a tiny air pressure sensor inside the device. When you draw air through the mouthpiece, the suction creates a slight vacuum. The sensor detects that pressure drop and closes an electronic switch, sending current from the battery to the heating element. This all happens in a fraction of a second.
The heating element is a small strip or coil of metal embedded near the top of the liquid reservoir. A wick, usually made of cotton or synthetic fiber, sits in the center of the reservoir and draws liquid toward the heating element through capillary action, the same force that pulls water up a paper towel. When the current flows, the metal heats up and vaporizes the liquid in contact with it. You inhale the resulting aerosol, and when you stop drawing, the pressure sensor opens the circuit and the coil cools down.
What’s in the Liquid
E-liquid has four basic ingredients: propylene glycol (PG), vegetable glycerin (VG), nicotine, and flavorings. PG and VG are the carrier liquids that make up the bulk of the mixture, and their ratio shapes the experience in distinct ways.
PG is thinner and produces a stronger “throat hit,” that sharp sensation at the back of your throat that mimics smoking. In controlled studies, liquids with a 70/30 PG-to-VG ratio were rated as having significantly better throat hit than 50/50 or pure VG mixtures. PG also appears to deliver nicotine more efficiently: at high PG concentrations, blood nicotine levels rise faster and higher, though participants in studies found those high-PG liquids less pleasant overall.
VG is thicker and sweeter. It’s widely associated with denser vapor clouds, though interestingly, when researchers tested this perception in a controlled setting, participants didn’t actually rate cloud production differently across PG/VG ratios. The difference may be more noticeable in higher-powered devices where more liquid is vaporized per puff.
Freebase Nicotine vs. Nicotine Salts
Nicotine in e-liquid comes in two forms, and they behave very differently in your body. Freebase nicotine is the traditional form: it’s harsher at high concentrations, which limits how much you can comfortably inhale. Nicotine salts, created by combining freebase nicotine with an organic acid like benzoic acid, are smoother and absorb into your bloodstream much faster.
In a clinical study by PAX Labs, a 2% nicotine salt solution produced peak blood nicotine levels three times higher than 2% freebase nicotine. Research with nicotine lactate, another salt form, showed similar results. This rapid, high-peak delivery is what makes small, low-powered pod devices feel satisfying despite producing relatively little vapor. It also makes them more addictive.
How Coil Design Affects the Experience
Traditional vape coils are a single wire wound into a spiral. The wire heats along that narrow spiral line, which means only a small portion of the wick is in direct contact with the hot surface. This can create uneven heating and takes roughly a second to reach the right temperature.
Mesh coils, now common in most devices, use a thin metal sheet punched with tiny holes, creating a net-like structure. The perforated design puts a much larger surface area in contact with the wick, which does two things: it heats the liquid more evenly (producing more consistent flavor) and it reaches operating temperature almost instantly. The moment you inhale, the mesh is already hot.
Mouth-to-Lung vs. Direct-to-Lung
Vapes are designed around two fundamentally different inhaling styles, and the hardware differs to match each one.
Mouth-to-lung (MTL) devices mimic the draw of a cigarette. You pull vapor into your mouth first, then inhale it into your lungs. These devices have a narrow mouthpiece and restricted airflow, and they run at low wattage, typically under 20 watts. They produce modest vapor and work best with higher-nicotine liquids.
Direct-to-lung (DTL) devices have wide-open airflow and larger mouthpieces. You inhale directly into your lungs in a single breath, more like breathing through a straw than sucking on one. These require significantly more power to vaporize liquid fast enough to fill that larger airflow, which means higher wattage, more liquid consumption, and bigger clouds. DTL setups are usually paired with lower-nicotine liquids because the sheer volume of vapor delivers more nicotine per puff.
What Heat Does to E-liquid Chemistry
The vaporization process isn’t chemically clean. When PG and VG are heated, they can break down into byproducts including formaldehyde, acetaldehyde, and acrolein. At low power (around 10 watts), these byproducts form in very small quantities. But when power exceeds 40 watts, their production increases exponentially. Some devices, particularly at 60 to 75 watts, can push coil temperatures above 500°C, far beyond the normal operating range.
The metal in the coil itself plays a role. Research has shown that the presence of metallic wires causes carbonyl compounds (a category that includes formaldehyde) to form at temperatures below 250°C, compared to 460°C without metal present. This means the coil isn’t just a passive heat source. It actively catalyzes chemical reactions in the liquid.
Flavorings add another layer of complexity. Sucralose, a sweetener used in many e-liquids, can produce toxic chlorine-containing compounds when heated. Fruity esters like ethyl butyrate (responsible for fruit-forward flavors) can convert to carboxylic acids during vaporization, and under “dry hit” conditions where the wick runs low on liquid, temperatures spike high enough to produce more dangerous breakdown products. Both sucralose and the flavoring compound triacetin can also accelerate the breakdown of PG and VG themselves, increasing formaldehyde and acrolein output from flavored liquids compared to unflavored ones.
The Battery Inside
Vapes use lithium-ion cells with high power density, meaning they pack a lot of energy into a small space. This is necessary because the heating element demands short, intense bursts of current, and the battery needs to outlast the liquid supply in the reservoir. In disposable devices, the battery is sized to die around the same time the liquid runs out.
Battery safety has been a real concern. The U.S. FDA, along with UL (a safety certification organization), the Consumer Product Safety Commission, and Health Canada developed a voluntary standard called UL 8139 specifically for vape electrical systems. It covers battery management during normal use and foreseeable misuse, mechanical stress, accidental activation, and environmental resilience like heat and humidity. The FDA has stated that devices meeting this standard carry significantly reduced risk of battery-related incidents, though compliance remains voluntary.