Both open-cell and closed-cell spray foam are applied as a liquid that quickly expands to fill any gaps or voids. Open-cell spray foam expands more than closed-cell foam, and many of the bubbles (which provide the material's insulation value) break open. This means that it offers a lower R-value of about R-3.5 per inch compared to R-6 to R-7 per inch for closed-cell spray foam. Its resistance to moisture and airflow are also reduced, making open-cell spray foam less capable of air sealing and waterproofing. Closed-cell spray foam is the better choice for insulation, air sealing and waterproofing performance, though it is more costly than open-cell foam.