What is a backer rod?

A backer rod is a flexible foam rod used to fill gaps and joints in building construction or other applications. It is typically made from closed-cell polyethylene foam or similar materials and comes in various sizes and shapes to fit different types of gaps.

Backer rods are inserted into the joint or gap before applying caulk or sealant to provide support and control the depth of the sealant. They help ensure a proper seal by preventing the sealant from sinking or adhering to the bottom of the joint, which can lead to failure.

Backer rods are commonly used in a variety of applications, including sealing windows, doors, expansion joints, concrete joints, and cracks in pavement. They are also used in roofing applications to fill gaps and prevent water intrusion.

Overall, backer rods are an essential tool for achieving a watertight and airtight seal in construction projects and other applications where sealants are used.