Steadman,to be honest I don't remember,I think a boat site.If you do a search for mini cell foam,you will find plenty of places.I shoot bows from 50-55 # and heavy carbon arrows and a 3" slab will stop those arrows about 2/3rds of the way in.It will stop most 10 gpp arrows out of 60 # bows.4" thick would give added insurance.A side note is that it's the perfect foam for inside the hood of bow quivers.I can cut out the quiver foam on a band saw and shape with rasp and sandpaper.It carves and rasps really well.Once you see it,it is obvious that many quiver makers are using it.What I have done is buy two slabs and when the center of one wears out,make a new center by cutting the second slab into 4 equal squares.That makes 4 replacement centers.I use several straight pieces of coat hanger wire to stab through the side of the target slab,into the new center to hold it in place.