I've thought about that, but the materials cost would be very high. I've seen a very cool self skinning foam that would work just about like a NERF. You'd have to use a flexible primer to paint it, but it would be very cool. You'd hve to spend about $100 on foam, not to mention the mold.
I was actually considering making a foam jet pack for the film I am shooting...but I don't know practical it would be. I was thinking of making a copy of my jet pack from that foam stuff you spray and it turns hard...just for a couple shots where I'm thrown and I "bust" my pack.
I decided I'm just going to use my crappy old cardboard one.
the problem you'll have with expanding flexible foam is the shrinkage. I cast a flexible foam jet pack last year for a fanfilm but it shrank unevenly and warped in a silly way.
I now cast my jepacks in resin and expanding RIGID foam and they are featherlight.
I suppose you could cast a urethane rubber into the mold but, like someone said, the cost is pretty high.
If someone were to buy me a gallon kit I'd try it from my molds.
if you have a mold of a jet pack just pour in casting latex,it is used for making halloween masks (fill it to the edge/top of mold and vibrate the bubbles out with your hand or rubber mallet lightly tapping the sides of the mold to bring the bubbles to the surface)and let it sit for about 30 minutes for a good skin,pour excess latex back into latex container. Now just let it cure over night and once its cured just carefully fill it with that great stuff spray foam from your local wally mart.If it shrinks just squirt alittle more here and there.If it rises to much simply cut it off once it has cured. Also if you want the latex skin to be more rigid there is fillers you can add to it. One is called cabasil.If you didn't want to use the spray foam you could just glue in upolstery foam pieces cut to the shape of the iside of the latex jet pack Hope this helps someone Just pm me if you have any other questions about this method. I make latex masks.
Cris has amazing stuff! I have his 3po
True a latex jet pack would be a good option BUT latex is really selective about curing. It won't cure on a silicon or urethane surface (well it WILL but it would take MONTHS). Latex cures best on plaster/hyrdrocal. And the only way to get a hydrocal negative of a jet pack body would be to have a wax or clay casting out of a traditional rtv mold that you pour stone over.