Open cell spray foam is soft, semi ridged spray foam. Designed for indoor use only, it is best used above grade. New construction, remodels and pole buildings are a great place for open cell spray foam.
It will have an R-value of 3.5 to 4 per inch. R-value only tells part of the story. Open cell spray foam can stop 94% conductive heat loss at only 4 inches of depth. Its air sealing capabilities are the real benefit of open cell spray foam. When sprayed into place, open cell expands about 100 times itself, sealing and filling small cracks and crevices, stopping air flow from drafty winter days.
Other advantages of open cell include sound control and a lower installed cost than closed cell spray foam.
While other contractors will bash open cell, it does not natural absorb water. Open cell is hydrophobic, it naturally repels water. If it is submerged into water, it will absorb water. So, unless you have a major leak, it will not just “soak up” water. Open cell spray foam takes more skill to spray to proper depth and may require trimming the cavity, A lot of foam sprayers push closed cell spray foam, because they don’t spray open cell foam much, so they don’t have the skills to spray it to depth, resulting in lots of trimming and waste.