We are working some designs of wood frame building with corrugated steel cladding. What is common in our area is using this Aluminum foil material that is stuck to about 1/8" of foam, and this material is pinched between the frame and steel cladding. Builders put wild claims on this stuff, like "R30+". I need to get right down to the science to either confirm or debunk this material. My real concern is it is a moisture barrier with no perm rating. I feel like this product likely works great if there is no other insulation or wall finishes added, but when that occurs, this could trap moisture in the wall. As well, I just cannot buy into this "radiant barrier" thing as there is no air gap! It is in contact with the steel. I have tried to reach out to some other engineers, but the ones that are more publicly known are too "busy" to have this conversation. I need to solve this or make a decision in the next week. My plan was to spec Tyvek. You most certainly want an air control layer between the steel and frame.

Hello, I believe you have resolved the issue. If the job is still in progress, talk to your builder about your plans and see if he is satisfied. Simply follow your instincts, and remember to wear a fall arrester when working at heights.

If you haven't already, contact Joseph Lstiburek, Ph.D., P.Eng., ASHRE Fellow at Building Science Corporation. Here is a link about him: https://www.buildingscience.com/users/joseph-lstiburek