There are Minecraft swords made of foam for sale...and they are about $20.
Here's the DIY for $6.
(I'm too cheap to throw down $20 for foam)
I got mine at Hobby Lobby.
The black comes in a much thicker option for $1.27 each...I used 2.
I used 2 gray as well for $.87 each.
And 3 inches of brown and 1 additional thin sheet of black.
I printed off this iron sword the size I wanted it...taped it together and cut it out.
Then used it as the pattern.
I traced it on 2 layers of black and 2 gray.
(I cut them all out separately...and trimmed them up at the end)
I used a hobby knife to cut them out.
Once I got my layers cut, I cheated and used Sticky back foam.
You can just use regular foam and your hot glue gun.
Cut 1 inch strips of black, gray and 3 squares of brown.
I had some 2 inch pieces for the longer parts, you could
just piece it all in with 1 inch squares though.
between the 2 thick black layers of foam.
Just hot glued them right in there to add stability.
Then I sandwiched all the layers together with hot glue.
You can see the edges didn't all line up perfectly.
So I plugged in my new Hot Knife!
It's got all the attachments for wood burning, and this hobby knife!
It heats up fast and can cut through all these layers of foam like butter!
Finished! Now go craft something!