Thanks! The green parts are the printed parts. There is actually a printed mouthpiece that goes with it as well, but it wasn't done printing at the time of the picture. The white stuff is indeed PVC (well, some PVC some PEX). My printer can't print a straight section of tube that long with a sufficiently smooth surface to work as a slide or a tuning slide (very few can print that length, and none that I know of could print one smooth enough) so the use of PVC for the slide and the tuning slide was due more to a technical limitation than any particular design aesthetics. The join union fitting and the back piece of pipe are standard 1/2" schedule 40 PVC tube. That could have been printed, but I kept snapping the tube pieces back there, so I went with something stronger to make it a more usable instrument. It is indeed operable.
It actually sounds like a real trombone, though somewhat muffled since you don't get the resonance you would from the metal. The bell is also slightly undersized due to the maximum printing size of my existing printer, so it doesn't project quite as well as it should. I'm still getting some air loss between the inner and outer slide that I need to resolve, but it is playable and recognizable as sounding like a trombone. I'm experimenting with heat shrink tubing on the inner slide to see if I can get a closer fit. if I can eliminate the air leak there then I think it is actually a viable instrument. The main slide works, the tuning slide works. It needs a better water relief valve at some point, and a slide lock, but I didn't think I was going to have time to design those bits before the contest.
I do play trombone, though I am a bit out of practice. Played all through school up to College I used to be pretty good. I can still play a tune on a real trombone pretty well. I've heard worse sounding trombones, though I don't expect to see the major trombone players of the world switch over to this model immediately.
People will be able to print one of these for themselves as soon as the place we're supposed to upload the files to for the contest fixes their 5 file upload limitation so I can upload all 11 pieces of the design. I'm considering uploading this one to shapeways as well so people without their own 3d printer could order one eventually.