All-Metal was recommended to me by the guy I was going to pay to do this job, after he convinced me I could do it myself. However, fiber-filled is prescribed in the directions on the Lord Fusor panel adhesive. Also, I read somewhere that All-Metal isn't better than fiber-filled. It's aluminum, so it has different thermal expansion than steel. Apparently the modern plastic fillers are a better match to the expansion properties of the steel. Someone who knows better can feel free to weigh in here.