Backer rod is a polyethylene foam rod used for a variety of construction purposes. When applying liquid sealant, backer rod is used to maintain proper joint design. There are different types of backer rod, including a bi-cellular soft-rod, closed cell backer rod, high temperature and open cell rods, all used for different sealant applications. Soft rod is non-gassing and most commonly used to prevent sealant from bubbling. Backer rod is extremely flexible; it is available in a variety of different diameters and custom shapes. Product Category: Expansion Joint Systems, Joint Fillers