This is for a 12"x12" square of 2" thick opencell charcoal firm foam. This is the industry standard for larp/boffer arrowheads for games like Dagorhir and Belegarth.
If you want arrowheads, these will make 16 smaller 3"x3" squares you can mount into your closed cell base design.
You can also use these for simple round dagger stabbing tips. I would not suggest using these for sword stabbing tips, it's outdated tech. Although I personally like to use a thicker block of opencell foam, this can also be used for javelin tips.
I cut these squares out by hand from a larger sheet of the foam.