HouseChalk
Open-cell foam
Open-cell foam is a softer type of spray foam insulation with lower density that allows vapor to move through it.
Why it matters
It is more affordable than closed-cell and fills spaces well. It is not a vapor barrier, so it needs the right wall design to avoid trapped moisture.
Where people get this wrong
Open-cell foam is not waterproof. It should not be used below grade or in flood-prone areas. In hot-humid climates, vapor control details matter.
Real-world example
A contractor sprays open-cell foam in an attic roofline. The foam expands and seals, but vapor can still move through it if the house needs to dry to the outside.
Where this hits your build
This affects comfort, energy costs, and indoor air quality. It gets locked behind drywall, so decisions here need to be right before finishing starts.
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