Backer rod is a nonabsorbent, compressible rod foam rope used to partially fill large cracks, gaps, and joints before applying sealant. Can be applied to horizontal or vertical surfaces. Use for expansion joints, curtain wall joints, partitions, log construction, pavement joints, precast. Can also be used as a temporary seal to control sealant depth or to create a backstop. 3/4″ diameter by 20′ long.