Do it Poly 5/8 in. x 20 ft. Gray Foam Caulk Saver Backer Rod features resilient poly foam that provides an efficient fill or seal for large openings. This moisture-resistant backer rod helps save on expensive caulks and sealants while lasting for years. It is i for filling cement cracks, meeting joints, aluminum siding panels, and door and window frames. Additionally, it effectively seals foundation bases to protect your home. Model Number: C23HDI