I posed a question this week: In a mixed humid climate, do you use open cell foam exclusively or can you in fact use closed cell in some limited places. In speaking to a very experienced architect on the subject, he hands down believes that closed cell in the answer for the typical wall system design. My problem – I can only find science that refutes his claim. Closed cell foam is a vapor barrier that will not let moisture flow through the wall system. In our climate, where we do have two seasons, we cannot have a vapor barrier, or we will produce moisture issues. The only way to prevent moisture issues is to include a dehumidification system as part of the HVAC design, hope that dew point is not reached in the wall, and cross your fingers. While I do want a dehumidification system in every project, we know they don’t always get installed due to budget cuts. However, the bigger issue is when the building is shut down for a few days, people go on vacation and cut back the thermostat, schools are out for the summer, then the system is not running as designed. When this happens, you are going to have a mold problem. I cannot find any science to back up the claim that closed cell foam can be used here in our climate. If you want to give me some data, I would love to be able to achieve the higher R values that the product offers.