MgO cement (Magnesium Oxide); 6 mil poly vapor barrier required. Aluminum siding: 0.61 40 metal thickness: 0.11 : 0.61 40 full thickness, hollow-backed: Asbestos, corrugated paper pipe insulation: 1.4: ... I want to know how to calculate the U-Value and R-Value of 7 cms thick and 4,4 cms thick plastic bricks ( plastic mixing recycled bricks ...