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

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.

Open-cell backer rods are the most compressible and maintain their shape better than bicellular ones. They allow moisture to be absorbed. Although they withstand environments up to 500° F, they shouldn’t be used with hot-pour sealants, which can seep through the large cell size and damage the underlying surface.