Things keep changing for Pittsburgh's FLUX parties, even as the venerable event returns for the second time this year.

FLUX 15, this Saturday night at 8 p.m., has the usual mix of art, music and beer in a vacant commercial space, this time in two empty floors of a building on Sixth Avenue Downtown. There are two new, related features: a bike valet service and a commitment to make the party "green."

The bike valet service will allow visitors to ride bicycles to the party site -- above the Brooks Brothers store at Smithfield Street and Sixth Avenue -- and park them in a safe, guarded indoor space across Smithfield, in the former Barnes & Noble bookstore. The service, managed by Bike Pittsburgh, is free.

For the first time, all cups, bottles and even some installations -- created by local design firm SO-AD -- will be recycled. Paper products and marketing materials for the event were made on recycled paper and organizers are working with Restorative Events, a Pittsburgh-based green consulting firm on sustainability issues.

In addition, art from more than 20 local artists is featured across two floors of the building, with performances by more than 15 musicians, DJs and dancers.

Performers include: Pancreatic Aardvarks, Ana-Vey, the Hidden Twin, Pfunkt, Brotha Mike, J Sands of Lone Catalysts, Kelly Parker, Ketan Bakarania, Andrew "the Impaled," Devin Russian, the Weird Paul Rock Band, Discuss, In the Wake of Giants, Olivia Kissel of Zafira Belly Dance, Karl Hendricks Rock Band, Amoeba Knievel and Phat Man Dee.

FLUX started in 2000 as a way to celebrate art in under-used commercial properties. It went on hiatus in 2004, before forging a partnership with the Three Rivers Arts Festival and coming back for FLUX 14 in Braddock in April. Plans are to throw three parties per year, two in neighborhoods around the city and one Downtown during the arts festival, which ends Sunday.

SO-AD, a firm run by Carnegie-Mellon architecture professors David Burns and Jason Morris, has the task of gussying up the vacant space for the party. To do so, the pair is wrapping columns in transparent white, red and black stretch wrap to make default walls.

The stretch wrap will be illuminated to give off a "3D and spacial" look, Burns said, while also directing visitors to art spaces and lounge areas. The firm is using the plastic wrap -- which will be recycled after the party -- "to create rooms and create movement and circulation, without using drywall," Burns said.

Hours are 8 p.m. to 1 a.m. Saturday night. Tickets are $10, $8 for students, with free admission to children under 10 years old. Proceeds benefit participating artists.