Summer 2012: Props.... Making UFOs

For our galactic version of Romeo and Juliet we are working on in this year's workshop, we need 8 UFOs. These are for the smaller kids to wear during the "rivalry scene" and for a chorus of 4 of the older boys during the "love scene" choreography.
They need to be:

• lightweight
• easy to put on and off 
• cheap to make (!)

I'm thinking they can be worn around the waist, with shoulder straps to stop them slipping off. Something like this:


So we have had a series of ideas.
Idea one:
Two cardboard "cones" with tops cut off taped together, covered in tape or a thing layer of paper mache and spray painted silver

The snag:
No real snag, except finding enough cardboard boxes in a remote mountain village..... it's just too hot to contemplate at the moment (! but we may come back to this idea!)

Idea two:
We move on to a ready-made shape - the swimming ring. This, we think, might even be able to sit snugly on the hips of the bigger kids without shoulder straps. We buy two, in different sizes, wrap with tape as a base... and find them deflated in the morning. This creates a dilemma: are we back to paper mache (moving fast before the air comes out?) or should we abandon the idea?

Idea three:
Rubber rings filled with insulating spray foam! This was not an outright failure (before I embark on the debacle) but it wasn't an instant resounding success! The idea was to fill the ring with foam (blocking any air holes in the process) and wait for it to expand to fill the ring. If you are interested in this idea, a few observations:

• we filled the ring from various points, making a small hole with scissors where necessary
• you can't use th ready-made nozzle because of the valve (duh)
• the foam does not expand as expected (lack of air? foam plus air in a confined space means lack of room?)
• it takes longer to dry than expected (again, this may be lack of air - perhaps air holes would work?)
• blow the ring up first but be prepared to let air escape quickly as the foam expands - the ring will suddenly get very overfull!

In the end, after several days, the foam DID dry and the ring became firm all round, but it has air pockets (actually large gaps between the foam "blobs"). Sooooo.... if we hadn't come up with our next idea, I am confident this method would give results (in case anyone is researching the idea).... it just might need tweaking. Another idea, along the same lines (again for any foam fanatics out there) would be to blow the ring up and seal the edges and the valve with spray foam before smoothing with a cutter when dry.

Idea four (the One, if all goes well!):
Having mulled the cost of the spray foam and the swimming rings, we decided to have one last ditch attempt at finding a cheaper solution. Having rung a nearby car tyre garage, we are now the proud owners of 16 punctured inner tubes... which (once we have mended them) we will hopefully be able to inflate, spray silver and decorate with... yogurt pot "ufo lights" and the like..... We'll see how it goes...

Any ideas for making a UFO costume/prop? Ever used spray foam for a project? Tell us all about it in a comment!