Elephant skin helps protect your roof from everyday activities in your home like showering, cooking and doing laundry which creates hot moist air in your home. A good portion of that moisture is extracted into the attic by exhaust fans and then to the outside through your attic vents. Keep in mind, heat rises so a percentage of the moisture will naturally find its way through building materials such as the sheathing or plywood that creates your roof deck. Underlayment acts as a vapor barrier. This is where roofing underlayment comes into play. Some of the moisture will excrete through the asphalt roofing shingles and escape completely. The moisture that does not is now trapped in between the shingle and the roof deck. Underlayment acts as a vapor barrier to keep that moisture from wreaking havoc on the wood surface. There is never enough condensation build up to create a running flow of water but a consistent wet condition will rot out the roof deck and cost you a lot of money! Using underlayment helps protect your roof to obtain the maximum roof life.