Polyester for fibre purposes is PolyEthylene Terephthalate, or simply PET.
PET is made by reacting ethylene glycol with either terephthalic acid or its methyl ester in the presence of an antimony catalyst. The reaction is carried out at high temperature and vacuum to achieve the high molecular weights need to form useful fibres. These PET fibres are melt spun.
Polyester Stratis membranes are available in either the natural white or the dope-dyed black fibre.
A polyester membrane offers the same advantages over polyester cruising laminates (Dimension-Polyant DC, Bainbridge CL, Contender ACL and Challenge PC) that a Technora Stratis sail has over a conventional panelled Kevlar construction, i.e. much better shape retention over a wider range. Polyester by nature is relatively stretchy so this helps keep the loads on sheets and attachment points down due to the elasticity of the sail.
PEN is the big brother of PET, it was invented shortly after PET but not commercialised until the 1990’s. PEN does provide a significant increase in modulus over PET, so it is very useful in those sail classes limited by Class Rules to lower the modulus of fibres (or simply “polyester” fibres)
PEN is unfortunately not UV stable and should only be used in conjunction with proper UV blocking surfaces GPx 0.5mil UV film, GPx 0.75mil UV film, GPc 0.5, GPc 0.75, and the ULx surfaces.