It's foggy outside the Henley Vaporium in New York City's SoHo neighborhood. Gray clouds, swirling like ghosts, cling tightly to the sidewalk and century-old brick buildings.

The haziness from the street matches the air inside the shop. It's a different type of cloudy, though — lighter, with a sweet aroma. Water vapor from e-cigarettes. "You can barely see two feet in front of you when these guys are in here," laughs Peter Denholtz, the shop's co-owner.

See also: Everything You Need to Know About Electronic Cigarettes in One Minute

He points to a handful of twenty-somethings near the back. The men and women, most of whom don button-up shirts and flat-brim hats, chat anxiously around a glass counter covered with screwdrivers, wires and small metal tubes.

The scene looks like a snapshot from a high school shop class. They discuss "heat compression" and "propylene glycol."

Kyle Yan, 20, left, fiddles with a rebuildable atomizer at Henley Vaporium in New York City.

The group is part of Denholtz's customer base, which has created hobbies out of rebuilding and customizing "mods," metal tubes, similar to e-cigarettes, designed for "vaping" flavors and nicotine. By hacking these devices, they're able to produce stronger flavors and — more importantly — create more impressive vapor clouds.

Some enthusiasts mix their own flavors to share with friends; most hang out at the shop every night to exchange ideas and show off their newest upgrades.

Since the store opened in September 2013, Denholtz says, the majority of his customers have been smokers hoping to quit. Some come in looking for a cheaper alternative to hookah.

This new rebuilding trend, which he refers to as a science-rooted subculture, is only beginning to grow in popularity. Denholtz is just trying to keep up.

Nick Yuan, a 'vapologist' at Henley, puffs on a vaping pen behind the counter

"I'd say a good 20% of the people who come in here want to rebuild like this," says Tristan Ambat, 25, a "vapologist" at Henley. The title's even stitched into his white lab coat. For the most part, he specializes in customizing atomizers, a central component in both e-cigarettes and mods. Today, surrounded in a cloud of white vapor, he's rewiring the insides of one device.

To start, he takes a mechanical mod and a rebuildable atomizer; the former sends voltage from the device's battery to the atomizer. You can buy both at a vape shop or online. Prices vary. Depending on the models, you'll pay around $30 for the cheapest.

Ambat says most people like to lower the standard resistance, measured in Ohms, to send more heat to the device's coil. Doing so creates more heat for the inhale and a larger vape cloud for the exhale.

"You just open your atomizer. On the base are the coils," he says. "Unscrew them and slip your own wire through the small holes."

Mods come with different numbers of coils. The one he's using contains one coil, but some go as high as eight. More coils means more potential power.

He adds the wire — heating resistance wire is best, he says — and tightens the coils. He uses an app called Ohm's Law to check the Ohm level; it also calculates watts and amps. This device's Ohm level measures .08, below the standard 1.2 on most models.

"This is good. This means I'll get a little more heat than normal," he says, "and as you can see, it says I'm pulling about 4.6 amps of my battery."

Battery powers vary by device, too. To avoid overheating, it's best to use batteries with amps 14 or greater. Ambat uses a 30-amp battery. If he'd used a smaller one — say, an eight-amp battery — it'd be too close for comfort if the Ohm's levels pulled close to five amps, as they are now.

Next up, cotton creates a makeshift wick. "Organic cotton is essential. Most 100% cotton has bleach in it, so you don't want to be inhaling that," he says.

Organic cotton also helps bring out the most flavor. He tears off a small piece, rolls it into a wick and drops in a few dots of liquid flavor.

And that's it. Ambat takes a drag and exhales. A sweet-smelling gray cloud, grander than most others in the shop, swirls playfully and vanishes above us.

"This is my friend's blend. It's vanilla custard," he says of the flavor. "It's really good."

Ambat says it's easy to make your own flavors. The basic ingredients are propylene glycol and vegetable glycerin; from there, you can mix it with either candy flavoring or natural food extracts. You can add nicotine if you want, he says, but it's certainly not required.

Looking like Rick Ross and smelling like ice cream at the same time? Not a bad deal.

Denholtz, 53, cofounded the shop with Talia Eisenberg, 27, to cater to a crowd of customers hoping to quit smoking tobacco cigarettes. Denholtz was a smoker for 36 years until he switched to e-cigarettes a few years back. Since switching, he hasn't smoked a traditional cigarette in four years.

"The original purpose for this whole shop was health reasons. Talia and I both had great experiences with these, and we wanted to help people looking to quit," he says.

They do, for the most part. A hefty number of the shop's customers come in looking for supplies for vaping pens or basic e-cigarettes. Those looking to quit smoking do so gradually. There are different milligram levels of nicotine the store uses to measure its cigarettes. Someone used to smoking a pack per day, for example, can start by smoking an e-cigarette with 24 milligrams of nicotine. They reduce the levels after a few days, to 18, to 12, to 6, and eventually to zero.

The "scene" aspect — rebuilding and customizing — is new to Denholtz. Most of the mods and atomizers he sells are based on the recommendations of his hippest customers. But he's embracing the trend, even learning a thing or two in the process.

Other vape shops have opened up in the city over the past six months. At the moment, there are three in Manhattan, two in Brooklyn and one in Queens. The community expects more to pop up in 2014. And although the city recently passed a bill to limit public e-cigarette use, which will go into effect April 29, Denholtz says he's not concerned. Vaping lounges are exempt from the ban, under the premise that cigar bars are exempt from most smoking bans.

Since 2010, an annual nationwide festival called Vape Fest comes to different venues across the country. It's scheduled this year for March 21-22 in Washington, D.C.

Online, there's also a prominent vaping community. Groups on Facebook and Reddit serve as discussion boards or, in some cases, meetup vehicles. Hashtags like #VapeLife and #VapeTricks are popular for posting videos on apps like Vine and Instagram. Most feature footage of people blowing big clouds or performing tricks, like "smoke" rings.

The lights begin to dim at the shop. There's a jazz show tonight and the performer's running late. Nobody seems to mind. The vapor in the air creates a calming mood — warm, comfortable. Visitors lounge in chairs and couches circled around a center table; some puff on vaping pens at the newly opened cafe bar near the stage area. At places like these, with the low lights and warm humidity, stress seems to evaporate.

"This whole community is really growing. There are meetups at least once a month," says Kyle Yan, a 20-year-old student at Baruch College. "Everyone's really nice, and it's just a good way to meet people and learn new things. This is still new to me, but I love it so far."

The vanilla custard aroma from Ambat's mod still lingers in the air. The flavor might be sold at the store soon, he says, along with a few others his friends have concocted. Until then, it's free for anyone in the shop to sample.

"The best part about vaping? Things like this," he says, nodding his head toward a crowd of people near the bar.

The musician enters from the back and strikes a few chords on his piano. From the front of the store, you can hardly see him.

Images: Mashable. Video by Kenny Suleimanagich