Lead Wool is from strands of lead twisted loosely into rope form. It is more convenient to use than molten lead for caulking purposes because it requires no heating or pouring. Lead Wool properly packed is ideal for caulking and makes a tighter seal than molten lead which shrinks slightly after casting. It is ideal for filling openings where sheet, plate, or brick are not suitable and is positively the best way to fill crevices.

Lead wool is made by scratching fine strands from the surface of a lead disc. It is used for the caulking of joints in large pipes e.g. gas mains and in some specialist batteries.