Provide support for sealants in gaps—insert these backer rods into gaps and fill in with sealant.

Closed-cell backer rods restrict moisture from being absorbed. Use them with joints that have wide, even spaces. Cross-linked polyethylene backer rods can be used with tar, asphalt, cement, and other hot-pour sealants.

Bicellular backer rods are more compressible than closed-cell ones. They also restrict moisture from being absorbed. Use them with uneven joints where self-leveling is needed.