Expands to fill gaps, cracks, and voids, creating an airtight, moisture-resistant seal that improves energy efficiency and prevents drafts.From the ManufacturerGREAT STUFF Gaps & Cracks is a polyurethane-based insulating foam sealant that fills, air-seals and insulates small gaps (up to 1 inch) inside or out. But you probably guessed as much from the name. What you might not have guessed is how easy it is to use (thanks to the straw applicator) or how it expands to take the shape of cracks and voids to form a durable, airtight, and water-resistant bond that eliminates unwanted airflow and helps reduce condensation.