Closed-Cell Foam Backer Rod

Details

Closed-cell foam backer rods are used behind chinking and caulking.  Foam backer rod is essential for ideal joint design.  The rods provide backing for 2-point adhesion to sealants such as caulk or chinking. 

A thin layer of sealant stretches much better than a big ol' wad does.  If it can't stretch, it will either pull away from the log or pull apart, breaking the seal and increasing energy ($) loss.