Although some spray foams use CFCs as propellants/foaming agents, there are plenty of other options, including CO2 itself. There is lots of homework to be done before choosing a spray foam.
Urethane foam's high stabilized R-value is very attractive, because it means I should be able to get close to passivhaus standards with 6" walls. That would not be possible with cellulose. Additionally, as the house ages, I bet foam would hold its R-value better than cellulose + vapor barrier would.
Cans of Great Stuff use propane as the propellant, so they should be fairly low in terms of GWP.
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