[not yet finished axe]
Making my first heavy weapon. It's a 3lb, 5 foot long red/green axe with a custom fiberglass axe head core. I'm also trying to make the stabbing tip be the horn, like a real Danish axe. I really want to make it safe. I've got two more layers (marine foam) to put on before I test it. Hopefully it will be fine. Even with the two blue layers the medium hits I'm doing on my own leg seem to be fine, so that's a good sign.
 You're gonna want open-cell on that striking edge. Without it, the axe is gonna be straight-up solid
, and will hit like a brick. My unit has a red axe just like that (almost exactly the same build: harbor freight mats + blue).
 I'm not sure how puffy your marine foam is (I'm assuming like a seat cushion?). If it is a seat cushion, you might want something a little... friendlier than that. If not, then disregard this.