PEEKsil is polymer-sheathed fused silica tubing, available in outside diameters of 1/32 inch or 1/16 inch, and now in 0.36 mm. The sheathing polymer is polyether ether ketone (PEEK) that is mechanically strong and has ideal characteristics for sealing with conventional metal or polymer ferrule systems. PEEKsil may be used as a direct replacement for conventional stainless steel as well as a replacement for PEEK tubing used in liquid chromatography systems. The 0.36 mm OD material can be used directly in place of 0.36 mm OD fused silica tubing.