500FT Braided and Bonded, Black and Yellow Mason Line refill is made of durable nylon. A braided variety wound on a 1" diameter core. #18 nylon has a tensile strength of 165lbs. Mixed coloured options are 'bonded' for extra durability. Bonding is a process that coats the string to make it more wear, UV and water resistant. The line is stiffer and easier to tie knots and the ends won't fray as much when cut. Stringliner Mason’s Braided and Bonded Line is durable and available in a range of colours. Quality #18 Nylon Line (tensile strength 165 lbs.) Prevents twisting & knotting Ends won't fray as much when cut