In general, spray foam insulation is an excellent solution for filling in all cracks and spaces in your structure. You can also add it to existing walls without tearing them open.  Since open-cell spray foam has a much lower R-value, it’s not recommended for places with extreme temperatures. Heat and humidity can penetrate more easily. Open-cell works best for smaller, inaccessible areas due to its soft structure and ability to expand. It also dampens sound really well. In contrast, closed-cell spray foam has a higher R-value, so it’s perfect in places that have more extreme temperatures. It does not allow water to pass through. However, this could also mean it could conceal leaks.  In the end, whether you choose open-cell or closed-cell spray foam, it will depend on where you live, your budget, and your goals for the space you are insulating.