I'm not making molds, btw.
What I am trying to make is some floating marks.
(the wood was just thin ply sealed so I could put an eye hook on from the bottom)
I originally made them out of craft store Styrofoam and they looked AWESOME, but the damn ducks chewed them up. So now I'm on the look out for some other material that will not absorb water, I can paint them, will sit on water 24x7x365, and ducks, kids can't destroy. I really need 1" thick, as it was the best viability from a distance.
In searching local plastic, foam suppliers I was given a sample of HDU which looked and felt perfect. Being a closed cell foam, it won't absorb water, paint-able, durable, etc.., but damn expensive.
But I am open to ALL suggestions!!! I only need a minimum of 2'x4'x1" sheet, but 4'x4'x1" would be preferred so I could make extras.