I'n not an expert on this but when you are refering to density you mean thickness?The commercial felt wads for a 12 ga. are both 1/8" and 1/4" thickness.A 11/16" or 17mm punch should be the correct size for making your own.A12ga should be about .72 cal.Track of The Wolf and The Possible shop both carry 12ga. felt wads or one ofthe readers here may have some they can mike for you to make sure you get the correct punch.Felt expands when it's in the barrel for a tight fit even when pushed through a full choke.Hope this helps somewhat........Harold