What is the minimum required air gap/space for this product to work?

The foil side of the RoofingFoil™ must face an empty air gap/space of at least 1/4″. When possible, a 1/2″ air gap or more is ideal.

This air gap must be a true air space – nothing can be touching that foil side except air. No insulation, no vapor barrier, no foam, etc. For more info on why this has to be an air space for the product to work, watch this video about the required air gap for radiant barriers. The air space can be a dead air space or vented; if you have a choice between the two, a vented air space is better.