|When scanning for corrosion under the insulation, you are actually looking for wet insulation behind that shiny metal sheeting covering the insulation. So, when scanning for wet insulation, you will look at places where water could stay for periods of time or where the insulation will stay wet for a long time. A good time to do your scanning will be after a good rain, preferably doing this at night to eliminate solar effects on the shiny covering. The temperature difference between the wet and dry insulation will be small (~15 to 25 F). Your IR camera should be able to detect this temperature difference.