Oakum

Oakum is a preparation of tarred fibre used to seal gaps. Its main traditional applications were in shipbuilding, for caulking or packing the joints of timbers in wooden vessels and the deck planking of iron and steel ships; in plumbing, for sealing joints in cast iron pipe; and in log cabins for chinking. In ship caulking, it was forced into the seams using a hammer and a caulking iron, then sealed into place with hot pitch.

It is also referenced frequently as a medical supply for medieval surgeons, often used along with bandages for sealing wounds.