I used a combination of 1/2 inch and 1 inch R max polyisocyanate insulation placed over the original foam insulation. Some places I could use the thicker and some I had to use the thinner stuff. I used aluminum tape to hold things in place until the headliner or ceiling materials were put in. Then they will do the job. I like the foil faces on the R max as where they \"see\" an air space they add significant insulating value, especially when it is warm outside. The job is done now, and I find a remarkable improvement in the comfort of the coach, both when cold and hot outside.