Last Saturday, Kevin and Debbie staged a rather impressive backyard carnival for Ethan's 5th birthday party, (inflatable jumphouse, bean-bag toss, petting zoo, etc.). I was invited to volunteer as the balloon animal guy. I'd never done balloon animals, but Debbie figured "if he can fold paper, he can certainly twist balloons".

## The Basics

So I picked up some balloons a few days before the event and started twisting. The basics were easy enough to discover:

Don't try to inflate the balloons with lung power, get a little hand pump.

Don't inflate the balloons all the way.

After inflating the balloon to the desired length, let a little air out to make it more flexible and easy to work with.

Don't be afraid—just start twisting and see what happens.

## The Party

And it was easy enough to make some simple shapes, (poodle, wiener dog and sword), without looking at any specific instructions. As it turns out, the kids at the party were more than happy with these—and there's definitely an advantage to sticking to models that are really quick when there's a line of kids waiting.

I'd meant to do at least some googling and find something more interesting to make, but I neglected to do that until just before the party. So I didn't have time to look at more than one site. I learned a baseball cap model there, and also a really intriguing volley ball from three balloons (pictured here). It's slick because none of the balloon knots or twists are visible—plus it actually works pretty well as a ball for bouncing around in the air.

I was feeling unprepared, so I kept twisting things in the car on the way to the party, (fortunately, I didn't quite cause an accident—no I wasn't driving, but the growing pile of balloons in the front seat did start distracting Stacy while she drove). On the way I figured out how to do a nice flower, (which, later at the party I made into a flower hat), and I also invented my first original design—a frog hat with oversized lips that can be squeezed to make it "talk". (Sadly, I was too busy doing balloons to actually take any pictures that day—and I'll have to figure out how to post video clips to do that one justice.)

## The Project

Anyway, the party was a lot of fun, and I was glad I could help out. When I got home I still had a couple of packs of balloons and I was still intrigued by that ball design, and wondered if similar ideas could be used to make something more elaborate. As with origami, I seem to be drawn more to the intricate geometric models rather than anything more organic like animals, (I think that's because my non-artistic brain can deal with "fold in half" much more easily than "fold at an angle that looks right for the beak").

My thoughts landed on Tom Hull's fantastic five intersecting tetrahedra origami design which I'd constructed once before as a gift, (I'll have to do it again and take a picture). So my pointless project for the weekend became recreating the structure from balloons.

I started by twisting each balloon into thirds, hoping I could get by with just inflating 10 balloons, (2 each of 5 different colors). But it was quite easy to see that balloons would be too thick at that size. It was also really hard to weave each tetrahedron while having to hold three different balloon segments to keep them from untwisting.

So next I attempted with full-length balloons. This would require 30 total, (6 each of the 5 colors), but would make it much easier to assemble, since each beam could be threaded independently, (much like the process with the origami model). But as soon as I built one tetrahedron, it was plain to see that the balloons were too thin at that large size and the whole structure would be far too loose, (but the kids did like using the resulting tetrahedron as a playhouse for the afternoon).

So the final structure uses 15 balloons, (3 each of 5 colors). Each balloon is inflated nearly all the way and then twisted once in the middle. This makes each segment in the final structure just short of 2 feet long while the balloons have a diameter of about 2 inches. And now that I'm typing instead of twisting, I actually went and read that Tom's origami design also uses a 1:12 ratio. So I could have saved myself some work experimenting by just reading that first. I did consider solving for the perfect ratio before starting with the balloons, but it's not easy for me to grasp the 3D geometries. Anybody care to help me solve that one? Tom also leaves the perfect ratio as a problem for the reader.

It's really a beautiful structure when complete. A single picture probably doesn't capture it very well. It's much more pleasing to be able to examine it in person and view it from many angles. Also, assembling the structure is actually a fun puzzle to solve, and I think forces the solver to gain a new appreciation for some of the symmetries inherent in the design. It had been 2 or 3 years since I had done this in origami, and I really had to learn the model all over again before I could get everything threaded correctly.

Posted Tue 05 Jun 2007 11:07:02 AM PDT