This is a very soft cotton caulking of the very best quality. Made from eight strands loosely left hand twisted to form an uncompressed diameter of about 8 mm. Cotton swells on contact with water to make a completely watertight seal. It is useful to wrap a bit of cotton caulking around bronze skin fittings and under bolt washers to prevent water ingress. Technical Specification: 100% pure soft cotton 8 strands.