Frost King 1/2 In. x 250 Ft. Poly Foam Backer Rod

Frost King's Poly Foam Backer Rod reduces the amount of caulk you need to fill large openings. It's non-absorbent. So, it works with virtually every type of caulk and sealant. It's also compressible which allows it to snuggly fill cavities. Just press in place, then caulk on top of it.