Like its name suggests, open-cell foam is made up of tiny bubbles, or cells, that are interconnected. The cells hold air, which provides insulation value – typically between R-3.5and R-4 per inch.
Like closed-cell foam, open-cell foam expands to fill gaps and cracks as soon as it’s applied. One of the first noticeable differences with open-cell spray foam is that it expands at a much greater volume. Typically this expansion is between 60 to 100 times its liquid state; as opposed to closed-cell spray foam’s expansion of roughly 30 times its liquid state.