M-D Building Products 1/2 in. x 20 ft. Caulk Backer Rod

The M-D Building Products 1/2 in. x 20 ft. Caulk Backer Rod is a flexible, non-absorbent, closed-cell polyethylene foam material designed for use prior to caulking. It acts as an effective filler in large joints, expansion cracks, and openings, helping to insulate, cushion, and prevent drafts and moisture intrusion. It provides a stable backing surface to ensure clean, professional caulking results. By filling excess joint depth, this pre-caulking backer rod prevents three-point bonding, allowing the sealant to adhere only to the joint sides for maximum flexibility and longevity. It is easy to trim with scissors and can be twisted together for extra-large openings, making it ideal for expansion joints in driveways, sidewalks, and various home weatherization projects.