Backer Rod is the product you need prior to chinking or caulking your log home. It not only acts as insulation, but repels moisture, too. Backer rod also serves as a bond-breaker between two logs and provides a structure against which you can apply chinking and caulk more uniformly in order to achieve an ideal joint.
Backer Rod is available in three shapes: Round, Triangle, and Trapezoid as well as an open cell formulation. You need to choose a shape depending on your log chinking or caulking situation, and/or the geometric shape of your logs. Round Backer Rod is most often used to push into checks and small cracks before log caulking is applied, and tends to be the least expensive Backer Rod.