as far as i know it was regular rockwool. it didnt burn per se, but blackened, smoldered and gave off a noxious fume right by the door (this firebox is seven feet long and hot hot hot!) which is why we tried to remove it. only a few smallish tufts (think the size of a dime) fell into a vat of over 30 gallons of boiling sap, which we tried to find and skim out. taste aside, if the fibers are filtered out will this be hazardous to consume? i realize the ridiculousness of this situation and that you fellas are not experts on this subject but it seemed the best place i could find on the internet to ask. i'm also inquiring in real life to real people who may have more expertise. thanks! cory