In a packed column, the carrier gas percolates through the porous bed and separation is achieved by moving the solutes apart. PTFE packing is fibrous and is made from machine-braided yarn. PTFE-based packing material is resistant over the range 0-14 pH and fluid temperature upto 258 °C. It also reduces friction during pump application. PTFE is limited to rotational surface speeds below 0.5 m/s due to its poor thermal conductivity and high thermal expansion coefficient. Porapak QS is a cross-linked polyaromatic resin which is capable to extract organic compounds and any trace metals associated with organic molecules.
For low temperature applications, a PTFE column offers the flexibility of metal with inertness approaching that of glass. This column is of a general configuration, and can be carefully bent to fit most instruments.