This was a quick project that my son and I worked on over Christmas break. He wanted to give a friend of his a present and he decided on a Minecraft sword. So we got some white foam board and laid out and cut the sword. We used 1 inch for the basis of the sword (each square of the sword is 1 inch). We then put some wood pieces in-between the two halves for some strength and then started taping.
I have made things like this in the past and I have found that a good way to make it durable is to wrap it in duct tape. We got some black and a blue/green color to match a diamond sword from Minecraft. I tore the tape in half lengthwise and just started wrapping it around. I think it turned out pretty well and it should last a long time.