Checkboxes better than radio buttons

[jidanni]

Isn't playground equipment often composed of more than just one material? As you see I have gone over to the Details panel and filled two in with a semicolon and then moved the screen back over to the Properties panel.

Wouldn't be wiser if these were all checkboxes and not radio buttons? That way we could pick more than one. And then the app could put the semicolon in for us in the details panel and we would just see two boxes checked in this image.