Choice of Casting Compound?

Hi,


What is a good, lightweight, inexpensive, strong casting compound that
is translucent or transparent?  I would like to build 'swords' that
will stand up to grown men dueling with them.

I did some research, and I have found a few possibilities (eg:
Urethane Plastics, E-108 WC, etc...), but being inexperienced with
casting compounds, I would like your opinions.

Since I rarely check my email, I would appreciate it if you would
respond to this group.

Thanks in advance.