rotten cotton / mineral wool

Plumbing inspection passed the rough in today - and he told me to make sure I stuff the plumbing and electrical holes made through the floors/walls with Rotten Cotten for fire protection prior to insulation inspection. I have seen this in the walls all over the house but need to buy more. It appears to be a fiberglass insullation but actually is more gritty and I don't think it's fiberglass. It is a mustard yellowish color.

Only thing I can find is that it's other known as mineral wool or slag wool...

Any clue where I might find this or some other product I can use to stuff the holes for fire block. I was told by the inspector not to use foam as it won't pass the fire block inspection....

thanks for any help Justin

There is a caulk specifically made for fireblocking in holes like this. Sold at HD for sure. Check with your inspector to make sure he's amenable.

found it

Mikey,

Thanks... I did see that at HD... inspector wants mineral wool (rotten cotten).... I did find it at the lumber yard a few miles from the house....

Thanks...

Just curious... how old would you estimate your inspector is?