Polymers used in microfluidics are mainly transparent thermoplastic polymers. Most popular are PMMA (Polymethylmetacrylate), COC (Cyclo-olefin-copolymer, tradename “Topas”), COP (Cyclo-olefinpolymer, tradenames “Zeonor” and “Zeonex”), PC (Polycarbonate), and PS (Polystyrene). Topas and Zeonor have outstanding optical characteristics, very low water uptake, and extremely low permeability for water vapour. Furthermore, they withstand polar organic solvents like acetone and isopropanol, frequently used in life sciences.