The Perforated Soflo Max rigid dual wall pipe, with smooth interior and corrugated exterior walls for roadway use, provides a compression stiffness of 210 kPa or 320 kPa, depending on the selected diameter, up to 900 mm (36 in). The use of Perforated Solflo Max is ideal for collectors since the coefficient of roughness is lower than that the interior wall of corrugated pipes.