Packed columns the carrier gas percolates through the porous bed. In a packed column, separation is achieved by moving the solutes apart. Packed columns are made up of two main materials; stainless steel and Pyrex glass. Metal packed columns are more suitable for long and high carrier gas flow rates to tolerate the elevated pressures. Chromosorb W, a fragile white solid prepared heating the diatomaceous earth with a flux. The resulting fine structure is cemented over glass which results in large and irregular pores. HP is the classification of a support as high performance grade.