Tremco 1 Backer Rod

Backer Rod is a resilient open cell, polyethylene foam. 

Used as a backing and thickness control device for elastomeric and other cold-applied sealants. Its use as a backup material eliminates the need for a bond breaker, and helps to control the depth of the sealant. Because the sealant will not bond to the backing rod, it can stretch and recover with joint movement, while minimal stress is put at the points of adhesion to the substrate.