Open Cell Backer Rod is a foam material used to fill large checks and gaps between logs. It also provides support for chinking and sealants. Open Cell Backer Rod is for interior use only.

Its primary purpose is act as a "bond-breaker" and promote two-point adhesion (see diagram), giving the joint and sealing material the ability to compress and expand as logs move.

Sealants and chinking do not adhere to the backer rod - only to the log surfaces of the joint - allowing for movement without damaging the sealing material.

Open cell backer rod is a little easier to install than closed cell backer rod because it is soft and pliable. It absorbs moisture so it causes the caulking and chinking to cure faster. Open cell backer rod is generally used only on the interior of the home. When open cell backer rod is used on the exterior of the home, if the caulking tears in any spot then the backer rod may absorb moisture, creating an ideal environment for rot.

Round backer rod can be used in almost every joint style except flat Applachian style logs. The round nature of the backer rod allows the caulking / chinking to adhere well to the wood, while the slightly thinner layer in the center allows the material to move with the logs. This also makes it so that any failure due to extreme movement will generally split down the middle of the bead line, allowing for an easy fix.