Casting a Large Sword (Hollow Plastic)

[Leash]

I'm new here but I'm not new to the world of costume and prop building. I've been building since 2000 but only recently in the past two years starting casting my props and moving away from wood and fiberglass.

My next project is to cast my fiberglass Buster Sword from Final Fantasy VII (6 feet long).

Right now it sits at about 8lbs, but I'm looking to make it even lighter. 8-10lbs may not seem like much, but its pretty heavy when it comes to balance. I've made another 7 foot sword (Guts sword from Berserk) and it feels like it 3 times heavier than the Buster sword, even though its the same weight (balance issue again).

So want to cast them into hollow swords. I've used Smooth-On in the past, Onyx for armor and Crystal Clear for a crystal fiberglass sword.

I'm trying to figure out which type of urethane to get. I want to go thin/light, with a hollow interior. Its got to be durable enough to withstand crowds of people bumping and pushing into it without it caving in and cracking/snapping.

Any suggestions on which product to get? Shared experience?

Also, has anyone tried Feather Lite? How thin can you go before it becomes to brittle?

 

[Nwerke]

I'd be surprised if you can find a urethane that's strong enough for anything other than static display, at the weight you're seeking.

Have you considered epoxy glass instead, maybe? Or even CF?