Makes professional joints that last. Helps fill in and insulate large caulk joints and allows the caulking to absorb more movement. Caulking adheres to the sides of the joint, but not to the filler rope, which allows the caulking to stretch and compress without tearing or pulling away thus extending the caulk's life and effectiveness. Made of closed cell poly foam. Minimum R value of 2.5/inch. Color: Gray.