Twenty-Two Inches Across
Standard party balloons disappear in a room with the lights down. At 22 inches these hold their own against a ceiling, and the metallic surface picks up whatever light is in the room and throws it back in patches. Clustered in threes they read as one large mirror ball from across a dance floor, which is hard to get from smaller rounds.
Helium Up or Air Down
Filled with helium they float, with the curling ribbon in the pack holding them at whatever height suits the room. Filled with air they can be taped to a wall, hung from a light fitting or piled in a corner behind the cake. Hosts without a tank get the same look by taping clusters flat along a backdrop and skipping the gas.
Valve That Seals Itself
The valve closes on its own once the nozzle comes out, so there is no knot to tie in foil and no tape over the neck. Inflating six takes a few minutes with a hand pump. At the end of the night the air comes back out through the same valve, and flat foil balloons store in an envelope rather than a box.
Y2K, Seventies and New Year
Silver mirror balls cover a stretch of party themes without any change of decor. The same six work for a seventies night, an eighties throwback, a Y2K birthday, a disco bachelorette, a graduation and the New Year countdown. Thick aluminum foil resists the slow leak that kills latex overnight, so a set inflated on Friday is still round on Saturday.