Helium Girl's costume costs more than some of the high-tech computer machinery in the Hydrogen Cave. Her everyday costume consists of a short red skirt, knee-high red boots, red blouse with poofy sleeves and pink feathery trim, and a yellow "He" monogram on the front of the blouse. She has a knee-length gossamer cape. She doesn't wear a mask - unlike Hydrogen Guy and Deuterium Boy, her "secret" identity is well known. Hell, it sells a lot of merchandise. Apparently there is a hat, but she refuses to wear it. There is also a floor-length evening gown version of the costume with a slit up the leg, and probably several other versions paid for with the Cave credit card.
Hair: blond, in curls
Eyes: blue
Height: 5' 9" (175 cm)
Weight: like, EXCUSE me?!

Helium Girl can mentally control the physical, chemical and nuclear state of the element helium; can control the physical and chemical structure of compounds that contain a "significant" amount of helium. Since helium doesn't occur naturally on Earth in any significant amount, and doesn't form chemical compounds anyway, her chemical powers are fairly limited here on Earth. Which is just as well, since she doesn't know any chemistry anyway. She has "super-atomic" senses of smell and taste, like Hydrogen Guy and Deuterium Boy. Briefly she can assume certain properties of helium at standard temperature and pressure: she can achieve short bursts of super-speed due to the helium atom's high mobility; low density of helium gas allows her to float (but not fly); she can briefly transform herself into a cloud of hydrogen gas, at a high energy cost. Her maximum short-burst super-speed is half of Hydrogen Guy's, and a factor of square root two less than Deuterium Boy's.

In addition to these powers that are basically analogous to Hydrogen Guy's and Deuterium Boy's, she can also fire thin beams or larger short pulses of alpha particles (helium nuclei emitted during radioactive decay).

She has both ballet (for poise) and karate (for creeps and grabby fan-boys) training, which combined with her floating abilities gives her a graceful and rather effective fighting style. Her triple lutz has to be seen to be believed.

Deuterium Boy trained her on the sabre and epée, but she's a lack-lustre swordswoman. Mostly she gets by with charm, style, and mid-air crane kicks.

Something called a cranberry helium fizz, although more often she can be seen packing an over-priced bottle of water.

Yolanda was a highly paid fashion model from California, until on her manager's advice, she went for some experimental helium-containing breast implants. (Not that I needed them, thank you.) There was a power surge with an MRI machine, and next thing you know she had helium powers. Somehow she hooked up with the Diatomic Duo, and when Hydrogen Guy went on four-month sabbatical in Ottawa in 2000, she became Deuterium Boy's - pardon me, the Deuterium Avenger's - sidekick.

Deuterium Boy and Helium Girl have a vaguely adversarial relationship. Basically, she thinks he's a dork and he thinks she's a ditz. They both, admittedly, have a point. She has a sisterly affection for him, though. (That's it .) Hydrogen Guy she mostly ignores - well, maybe not ignores, but they move in separate worlds. One of her best friends is Reaper, who's a good cook and fun to shop with. (As long as he, like, leaves the scythe at home.)

After Hydrogen Guy came back to Maple Ridge, she moved to Victoria and partnered with Deus Ex Machinas. Not much happening in the province's capital, though, and she came back to the mainland in 2002, setting up her crime-fighting Salon of Solitude in Vancouver's west end with her faithful manservant and buff ex-boyfriend Cato. (I mean, he's like, absolutely gorgeous and buff and stuff, but he's just so not, you know, intellectual.)