Backer rods are ideal,compressible and flexible backup PE foam products that are used to fill joints. People often use mortar, sealant or chinking around them to finish filling and create an airtight and watertight seal. They are non-absorbent and will resist oil, gasoline and most other sealants. They are compatible with most cold-applied sealants. Backer rods are used in tiling, flooring, decorative wall paneling, window sealing, stonework and counter steps.