According to an LSU AgCenter subfloor study, Insulating Raised Floors in Hot, Humid Climates, the most effective subfloor insulation in our hot, humid climate is rigid poly-iso foam board with all seams and penetrations sealed and polyurathane closed cell sprayfoam. However, because the labor and material costs of installing rigid foam board are so high, it is often a good solution to insulate the subfloor with closed cell spray foam (which also performed well in the LSU study). Because this foam is a vapor barrier, the moisture-laden air (water vapor) of southeast Louisiana cannot move through the insulation to bring heat and humidity into the home. Also, the foam insulation will not fall out or become home to small animals that might like to live in other types of insulation. Fiberglass insulation is never a good idea when it comes to insulating the subfloor.

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