FillPro Open Cell Backer Rod is a pliable open cell polyurethane (PU) foam material used for filling irregular joints. It is chemically inert and will resist oil, gasoline and most other solvents. The material will not stain, or adversely adhere to sealant or caulking materials. It’s available only in spool-less bags in 3/8” to 2” diameter. Open cell backer rod is commonly used in expansion and contraction joints, window glazing, curtain wall construction partitions, precast concrete assemblies and copings, parking decks and bridge construction. It’s compatible with virtually all known hot-pour and cold-applied sealant including silicone and rubber asphalt.