What is The Difference Between Open Cell and Closed Cell?

Open Cell, ½ lb. or low density spray foam cures soft and the irregular bubbles which form during the expansion reaction are broken or open. These pockets fill with air, and as such the R-Value of Open Cell foam is close to that of dormant air, around 3.6 per inch. Being spray applied as a liquid Open Cell foam conforms to any shape, but it is not a Code Approved Vapor Barrier with a permeability rating of over 400 ng. Closed Cell, 2 lb. or medium density spray foam cures rigid and the millions of microscopic bubbles which form during the expansion reaction remain closed and intact. This traps the reaction gases, and as such the R-Value of Closed Cell foam is close to that of the reaction gas, around 7 per inch. The Closed Cell structure is very strong; increasing shear and racking strength by 300%. Closed Cell foam is a Code Approved Vapor Barrier with a permeability rating of under 45 ng. Closed Cell foam stops both air flow through the wall and air flow within the wall cavity.