Closed-Cell Closed-cell spray foam insulation is known to be the more popular option between the two. It’s called a “closed” cell due to its high R-value. The R-value refers to the material’s capacity to insulate and resist heat flow. If the R-value is high, it results in greater insulation. Closed-cell spray foam can resist water from seeping into the insulation due to its high resistance. It is commonly used to insulate buildings and appliances because closed-cell spray foam is a denser material. Open-Cell Open-cell spray foam is similar to closed-cell in nature, except it has a lesser R-value. This spray foam expands as soon as it’s applied, making it the best option for hard-to-reach areas.