Closed-cell polyurethane spray foam has some pretty awesome qualities. It has a high R-value. It’s resistant to water, mold and insects. It expands into hard-to-reach nooks and crannies. Heck, it can even add structural support to walls and roofs. But it is expensive. So we spoke with a couple manufacturers and some pro insulators about where and when to use it, when to call in a pro with a truck-mounted unit, and when a portable kit is the best option. We also dug up some great installation tips to help you spray safely and get the most bang for your precious buck.