Here's a pretty decent guide for an balloon launch. In summary: don't use strings, call your alderperson or county rep first.

Hey eamondaly, that's a good link, I'd always wondered about that. Thanks.

I hear if you really want to be environmentally friendly you use only fresh baby seal gut for your balloons.

But if you really want to be green, balloon launches should be avoided entirely. Yeah, latex degrades rather quickly. But even simple party balloons can travel for hundreds or thousands of miles. Don't get me started on those mylar fuckers.

There have been many times, dozens at least, where I've been traipsing about in back country deserts and found balloon remnants, bits of string, mylar shards and more. Miles and miles and miles from civilization and the beaten path.

Suggested alternative: Bubbles! Rent a couple of huge-ass bubble machines. It's probably cheaper. Or if you really want that bright colors way up in the sky effect, hand out cheap kites to your guests. Or hire a professional kite flyer. Or hire a dove handler.

(I hope this hasn't come off as being a killjoy or holier-than-thou. Balloons are pretty, I dig 'em. One of these days I'm gonna try some cluster ballooning.)